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• Testing Asynchronous Methods in ASP.NET MVC

  In this article, I’ll first briefly describe the mechanics of asynchronous action methods and then move on to discuss how to test asynchronous methods.

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• Why would I need a using statement to Libary B extn methods, if they're used in Library A & it's Li

  - by Greg

  Hi, I have: Main Program Class - uses Library A Library A - has partial classes which mix in methods from Library B Library B - mix in methods & interfaces Why would I need a using statement to LibaryB just to get their extension methods working in the main class? That is given that it's Library B that defines the classes that will be extended. EDIT - Except from code // *** PROGRAM *** using TopologyDAL; using Topology; // *** THIS WAS NEEDED TO GET EXTN METHODS APPEARING *** class Program { static void Main(string[] args) { var context = new Model1Container(); Node myNode; // ** trying to get myNode mixin methods to appear seems to need using line to point to Library B *** } } // ** LIBRARY A namespace TopologyDAL { public partial class Node { // Auto generated from EF } public partial class Node : INode<int> // to add extension methods from Library B { public int Key } } // ** LIBRARY B namespace ToplogyLibrary { public static class NodeExtns { public static void FromNodeMixin<T>(this INode<T> node) { // XXXX } } public interface INode<T> { // Properties T Key { get; } // Methods } }

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• A Taxonomy of Numerical Methods v1

  - by JoshReuben

  Numerical Analysis – When, What, (but not how) Once you understand the Math & know C++, Numerical Methods are basically blocks of iterative & conditional math code. I found the real trick was seeing the forest for the trees – knowing which method to use for which situation. Its pretty easy to get lost in the details – so I’ve tried to organize these methods in a way that I can quickly look this up. I’ve included links to detailed explanations and to C++ code examples. I’ve tried to classify Numerical methods in the following broad categories: Solving Systems of Linear Equations Solving Non-Linear Equations Iteratively Interpolation Curve Fitting Optimization Numerical Differentiation & Integration Solving ODEs Boundary Problems Solving EigenValue problems Enjoy – I did ! Solving Systems of Linear Equations Overview Solve sets of algebraic equations with x unknowns The set is commonly in matrix form Gauss-Jordan Elimination http://en.wikipedia.org/wiki/Gauss%E2%80%93Jordan_elimination C++: http://www.codekeep.net/snippets/623f1923-e03c-4636-8c92-c9dc7aa0d3c0.aspx Produces solution of the equations & the coefficient matrix Efficient, stable 2 steps: · Forward Elimination – matrix decomposition: reduce set to triangular form (0s below the diagonal) or row echelon form. If degenerate, then there is no solution · Backward Elimination –write the original matrix as the product of ints inverse matrix & its reduced row-echelon matrix à reduce set to row canonical form & use back-substitution to find the solution to the set Elementary ops for matrix decomposition: · Row multiplication · Row switching · Add multiples of rows to other rows Use pivoting to ensure rows are ordered for achieving triangular form LU Decomposition http://en.wikipedia.org/wiki/LU_decomposition C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-lu-decomposition-for-solving.html Represent the matrix as a product of lower & upper triangular matrices A modified version of GJ Elimination Advantage – can easily apply forward & backward elimination to solve triangular matrices Techniques: · Doolittle Method – sets the L matrix diagonal to unity · Crout Method - sets the U matrix diagonal to unity Note: both the L & U matrices share the same unity diagonal & can be stored compactly in the same matrix Gauss-Seidel Iteration http://en.wikipedia.org/wiki/Gauss%E2%80%93Seidel_method C++: http://www.nr.com/forum/showthread.php?t=722 Transform the linear set of equations into a single equation & then use numerical integration (as integration formulas have Sums, it is implemented iteratively). an optimization of Gauss-Jacobi: 1.5 times faster, requires 0.25 iterations to achieve the same tolerance Solving Non-Linear Equations Iteratively find roots of polynomials – there may be 0, 1 or n solutions for an n order polynomial use iterative techniques Iterative methods · used when there are no known analytical techniques · Requires set functions to be continuous & differentiable · Requires an initial seed value – choice is critical to convergence à conduct multiple runs with different starting points & then select best result · Systematic - iterate until diminishing returns, tolerance or max iteration conditions are met · bracketing techniques will always yield convergent solutions, non-bracketing methods may fail to converge Incremental method if a nonlinear function has opposite signs at 2 ends of a small interval x1 & x2, then there is likely to be a solution in their interval – solutions are detected by evaluating a function over interval steps, for a change in sign, adjusting the step size dynamically. Limitations – can miss closely spaced solutions in large intervals, cannot detect degenerate (coinciding) solutions, limited to functions that cross the x-axis, gives false positives for singularities Fixed point method http://en.wikipedia.org/wiki/Fixed-point_iteration C++: http://books.google.co.il/books?id=weYj75E_t6MC&pg=PA79&lpg=PA79&dq=fixed+point+method++c%2B%2B&source=bl&ots=LQ-5P_taoC&sig=lENUUIYBK53tZtTwNfHLy5PEWDk&hl=en&sa=X&ei=wezDUPW1J5DptQaMsIHQCw&redir_esc=y#v=onepage&q=fixed%20point%20method%20%20c%2B%2B&f=false Algebraically rearrange a solution to isolate a variable then apply incremental method Bisection method http://en.wikipedia.org/wiki/Bisection_method C++: http://numericalcomputing.wordpress.com/category/algorithms/ Bracketed - Select an initial interval, keep bisecting it ad midpoint into sub-intervals and then apply incremental method on smaller & smaller intervals – zoom in Adv: unaffected by function gradient à reliable Disadv: slow convergence False Position Method http://en.wikipedia.org/wiki/False_position_method C++: http://www.dreamincode.net/forums/topic/126100-bisection-and-false-position-methods/ Bracketed - Select an initial interval , & use the relative value of function at interval end points to select next sub-intervals (estimate how far between the end points the solution might be & subdivide based on this) Newton-Raphson method http://en.wikipedia.org/wiki/Newton's_method C++: http://www-users.cselabs.umn.edu/classes/Summer-2012/csci1113/index.php?page=./newt3 Also known as Newton's method Convenient, efficient Not bracketed – only a single initial guess is required to start iteration – requires an analytical expression for the first derivative of the function as input. Evaluates the function & its derivative at each step. Can be extended to the Newton MutiRoot method for solving multiple roots Can be easily applied to an of n-coupled set of non-linear equations – conduct a Taylor Series expansion of a function, dropping terms of order n, rewrite as a Jacobian matrix of PDs & convert to simultaneous linear equations !!! Secant Method http://en.wikipedia.org/wiki/Secant_method C++: http://forum.vcoderz.com/showthread.php?p=205230 Unlike N-R, can estimate first derivative from an initial interval (does not require root to be bracketed) instead of inputting it Since derivative is approximated, may converge slower. Is fast in practice as it does not have to evaluate the derivative at each step. Similar implementation to False Positive method Birge-Vieta Method http://mat.iitm.ac.in/home/sryedida/public_html/caimna/transcendental/polynomial%20methods/bv%20method.html C++: http://books.google.co.il/books?id=cL1boM2uyQwC&pg=SA3-PA51&lpg=SA3-PA51&dq=Birge-Vieta+Method+c%2B%2B&source=bl&ots=QZmnDTK3rC&sig=BPNcHHbpR_DKVoZXrLi4nVXD-gg&hl=en&sa=X&ei=R-_DUK2iNIjzsgbE5ID4Dg&redir_esc=y#v=onepage&q=Birge-Vieta%20Method%20c%2B%2B&f=false combines Horner's method of polynomial evaluation (transforming into lesser degree polynomials that are more computationally efficient to process) with Newton-Raphson to provide a computational speed-up Interpolation Overview Construct new data points for as close as possible fit within range of a discrete set of known points (that were obtained via sampling, experimentation) Use Taylor Series Expansion of a function f(x) around a specific value for x Linear Interpolation http://en.wikipedia.org/wiki/Linear_interpolation C++: http://www.hamaluik.com/?p=289 Straight line between 2 points à concatenate interpolants between each pair of data points Bilinear Interpolation http://en.wikipedia.org/wiki/Bilinear_interpolation C++: http://supercomputingblog.com/graphics/coding-bilinear-interpolation/2/ Extension of the linear function for interpolating functions of 2 variables – perform linear interpolation first in 1 direction, then in another. Used in image processing – e.g. texture mapping filter. Uses 4 vertices to interpolate a value within a unit cell. Lagrange Interpolation http://en.wikipedia.org/wiki/Lagrange_polynomial C++: http://www.codecogs.com/code/maths/approximation/interpolation/lagrange.php For polynomials Requires recomputation for all terms for each distinct x value – can only be applied for small number of nodes Numerically unstable Barycentric Interpolation http://epubs.siam.org/doi/pdf/10.1137/S0036144502417715 C++: http://www.gamedev.net/topic/621445-barycentric-coordinates-c-code-check/ Rearrange the terms in the equation of the Legrange interpolation by defining weight functions that are independent of the interpolated value of x Newton Divided Difference Interpolation http://en.wikipedia.org/wiki/Newton_polynomial C++: http://jee-appy.blogspot.co.il/2011/12/newton-divided-difference-interpolation.html Hermite Divided Differences: Interpolation polynomial approximation for a given set of data points in the NR form - divided differences are used to approximately calculate the various differences. For a given set of 3 data points , fit a quadratic interpolant through the data Bracketed functions allow Newton divided differences to be calculated recursively Difference table Cubic Spline Interpolation http://en.wikipedia.org/wiki/Spline_interpolation C++: https://www.marcusbannerman.co.uk/index.php/home/latestarticles/42-articles/96-cubic-spline-class.html Spline is a piecewise polynomial Provides smoothness – for interpolations with significantly varying data Use weighted coefficients to bend the function to be smooth & its 1st & 2nd derivatives are continuous through the edge points in the interval Curve Fitting A generalization of interpolating whereby given data points may contain noise à the curve does not necessarily pass through all the points Least Squares Fit http://en.wikipedia.org/wiki/Least_squares C++: http://www.ccas.ru/mmes/educat/lab04k/02/least-squares.c Residual – difference between observed value & expected value Model function is often chosen as a linear combination of the specified functions Determines: A) The model instance in which the sum of squared residuals has the least value B) param values for which model best fits data Straight Line Fit Linear correlation between independent variable and dependent variable Linear Regression http://en.wikipedia.org/wiki/Linear_regression C++: http://www.oocities.org/david_swaim/cpp/linregc.htm Special case of statistically exact extrapolation Leverage least squares Given a basis function, the sum of the residuals is determined and the corresponding gradient equation is expressed as a set of normal linear equations in matrix form that can be solved (e.g. using LU Decomposition) Can be weighted - Drop the assumption that all errors have the same significance –-> confidence of accuracy is different for each data point. Fit the function closer to points with higher weights Polynomial Fit - use a polynomial basis function Moving Average http://en.wikipedia.org/wiki/Moving_average C++: http://www.codeproject.com/Articles/17860/A-Simple-Moving-Average-Algorithm Used for smoothing (cancel fluctuations to highlight longer-term trends & cycles), time series data analysis, signal processing filters Replace each data point with average of neighbors. Can be simple (SMA), weighted (WMA), exponential (EMA). Lags behind latest data points – extra weight can be given to more recent data points. Weights can decrease arithmetically or exponentially according to distance from point. Parameters: smoothing factor, period, weight basis Optimization Overview Given function with multiple variables, find Min (or max by minimizing –f(x)) Iterative approach Efficient, but not necessarily reliable Conditions: noisy data, constraints, non-linear models Detection via sign of first derivative - Derivative of saddle points will be 0 Local minima Bisection method Similar method for finding a root for a non-linear equation Start with an interval that contains a minimum Golden Search method http://en.wikipedia.org/wiki/Golden_section_search C++: http://www.codecogs.com/code/maths/optimization/golden.php Bisect intervals according to golden ratio 0.618.. Achieves reduction by evaluating a single function instead of 2 Newton-Raphson Method Brent method http://en.wikipedia.org/wiki/Brent's_method C++: http://people.sc.fsu.edu/~jburkardt/cpp_src/brent/brent.cpp Based on quadratic or parabolic interpolation – if the function is smooth & parabolic near to the minimum, then a parabola fitted through any 3 points should approximate the minima – fails when the 3 points are collinear , in which case the denominator is 0 Simplex Method http://en.wikipedia.org/wiki/Simplex_algorithm C++: http://www.codeguru.com/cpp/article.php/c17505/Simplex-Optimization-Algorithm-and-Implemetation-in-C-Programming.htm Find the global minima of any multi-variable function Direct search – no derivatives required At each step it maintains a non-degenerative simplex – a convex hull of n+1 vertices. Obtains the minimum for a function with n variables by evaluating the function at n-1 points, iteratively replacing the point of worst result with the point of best result, shrinking the multidimensional simplex around the best point. Point replacement involves expanding & contracting the simplex near the worst value point to determine a better replacement point Oscillation can be avoided by choosing the 2nd worst result Restart if it gets stuck Parameters: contraction & expansion factors Simulated Annealing http://en.wikipedia.org/wiki/Simulated_annealing C++: http://code.google.com/p/cppsimulatedannealing/ Analogy to heating & cooling metal to strengthen its structure Stochastic method – apply random permutation search for global minima - Avoid entrapment in local minima via hill climbing Heating schedule - Annealing schedule params: temperature, iterations at each temp, temperature delta Cooling schedule – can be linear, step-wise or exponential Differential Evolution http://en.wikipedia.org/wiki/Differential_evolution C++: http://www.amichel.com/de/doc/html/ More advanced stochastic methods analogous to biological processes: Genetic algorithms, evolution strategies Parallel direct search method against multiple discrete or continuous variables Initial population of variable vectors chosen randomly – if weighted difference vector of 2 vectors yields a lower objective function value then it replaces the comparison vector Many params: #parents, #variables, step size, crossover constant etc Convergence is slow – many more function evaluations than simulated annealing Numerical Differentiation Overview 2 approaches to finite difference methods: · A) approximate function via polynomial interpolation then differentiate · B) Taylor series approximation – additionally provides error estimate Finite Difference methods http://en.wikipedia.org/wiki/Finite_difference_method C++: http://www.wpi.edu/Pubs/ETD/Available/etd-051807-164436/unrestricted/EAMPADU.pdf Find differences between high order derivative values - Approximate differential equations by finite differences at evenly spaced data points Based on forward & backward Taylor series expansion of f(x) about x plus or minus multiples of delta h. Forward / backward difference - the sums of the series contains even derivatives and the difference of the series contains odd derivatives – coupled equations that can be solved. Provide an approximation of the derivative within a O(h^2) accuracy There is also central difference & extended central difference which has a O(h^4) accuracy Richardson Extrapolation http://en.wikipedia.org/wiki/Richardson_extrapolation C++: http://mathscoding.blogspot.co.il/2012/02/introduction-richardson-extrapolation.html A sequence acceleration method applied to finite differences Fast convergence, high accuracy O(h^4) Derivatives via Interpolation Cannot apply Finite Difference method to discrete data points at uneven intervals – so need to approximate the derivative of f(x) using the derivative of the interpolant via 3 point Lagrange Interpolation Note: the higher the order of the derivative, the lower the approximation precision Numerical Integration Estimate finite & infinite integrals of functions More accurate procedure than numerical differentiation Use when it is not possible to obtain an integral of a function analytically or when the function is not given, only the data points are Newton Cotes Methods http://en.wikipedia.org/wiki/Newton%E2%80%93Cotes_formulas C++: http://www.siafoo.net/snippet/324 For equally spaced data points Computationally easy – based on local interpolation of n rectangular strip areas that is piecewise fitted to a polynomial to get the sum total area Evaluate the integrand at n+1 evenly spaced points – approximate definite integral by Sum Weights are derived from Lagrange Basis polynomials Leverage Trapezoidal Rule for default 2nd formulas, Simpson 1/3 Rule for substituting 3 point formulas, Simpson 3/8 Rule for 4 point formulas. For 4 point formulas use Bodes Rule. Higher orders obtain more accurate results Trapezoidal Rule uses simple area, Simpsons Rule replaces the integrand f(x) with a quadratic polynomial p(x) that uses the same values as f(x) for its end points, but adds a midpoint Romberg Integration http://en.wikipedia.org/wiki/Romberg's_method C++: http://code.google.com/p/romberg-integration/downloads/detail?name=romberg.cpp&can=2&q= Combines trapezoidal rule with Richardson Extrapolation Evaluates the integrand at equally spaced points The integrand must have continuous derivatives Each R(n,m) extrapolation uses a higher order integrand polynomial replacement rule (zeroth starts with trapezoidal) à a lower triangular matrix set of equation coefficients where the bottom right term has the most accurate approximation. The process continues until the difference between 2 successive diagonal terms becomes sufficiently small. Gaussian Quadrature http://en.wikipedia.org/wiki/Gaussian_quadrature C++: http://www.alglib.net/integration/gaussianquadratures.php Data points are chosen to yield best possible accuracy – requires fewer evaluations Ability to handle singularities, functions that are difficult to evaluate The integrand can include a weighting function determined by a set of orthogonal polynomials. Points & weights are selected so that the integrand yields the exact integral if f(x) is a polynomial of degree <= 2n+1 Techniques (basically different weighting functions): · Gauss-Legendre Integration w(x)=1 · Gauss-Laguerre Integration w(x)=e^-x · Gauss-Hermite Integration w(x)=e^-x^2 · Gauss-Chebyshev Integration w(x)= 1 / Sqrt(1-x^2) Solving ODEs Use when high order differential equations cannot be solved analytically Evaluated under boundary conditions RK for systems – a high order differential equation can always be transformed into a coupled first order system of equations Euler method http://en.wikipedia.org/wiki/Euler_method C++: http://rosettacode.org/wiki/Euler_method First order Runge–Kutta method. Simple recursive method – given an initial value, calculate derivative deltas. Unstable & not very accurate (O(h) error) – not used in practice A first-order method - the local error (truncation error per step) is proportional to the square of the step size, and the global error (error at a given time) is proportional to the step size In evolving solution between data points xn & xn+1, only evaluates derivatives at beginning of interval xn à asymmetric at boundaries Higher order Runge Kutta http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods C++: http://www.dreamincode.net/code/snippet1441.htm 2nd & 4th order RK - Introduces parameterized midpoints for more symmetric solutions à accuracy at higher computational cost Adaptive RK – RK-Fehlberg – estimate the truncation at each integration step & automatically adjust the step size to keep error within prescribed limits. At each step 2 approximations are compared – if in disagreement to a specific accuracy, the step size is reduced Boundary Value Problems Where solution of differential equations are located at 2 different values of the independent variable x à more difficult, because cannot just start at point of initial value – there may not be enough starting conditions available at the end points to produce a unique solution An n-order equation will require n boundary conditions – need to determine the missing n-1 conditions which cause the given conditions at the other boundary to be satisfied Shooting Method http://en.wikipedia.org/wiki/Shooting_method C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-shooting-method-for-solving.html Iteratively guess the missing values for one end & integrate, then inspect the discrepancy with the boundary values of the other end to adjust the estimate Given the starting boundary values u1 & u2 which contain the root u, solve u given the false position method (solving the differential equation as an initial value problem via 4th order RK), then use u to solve the differential equations. Finite Difference Method For linear & non-linear systems Higher order derivatives require more computational steps – some combinations for boundary conditions may not work though Improve the accuracy by increasing the number of mesh points Solving EigenValue Problems An eigenvalue can substitute a matrix when doing matrix multiplication à convert matrix multiplication into a polynomial EigenValue For a given set of equations in matrix form, determine what are the solution eigenvalue & eigenvectors Similar Matrices - have same eigenvalues. Use orthogonal similarity transforms to reduce a matrix to diagonal form from which eigenvalue(s) & eigenvectors can be computed iteratively Jacobi method http://en.wikipedia.org/wiki/Jacobi_method C++: http://people.sc.fsu.edu/~jburkardt/classes/acs2_2008/openmp/jacobi/jacobi.html Robust but Computationally intense – use for small matrices < 10x10 Power Iteration http://en.wikipedia.org/wiki/Power_iteration For any given real symmetric matrix, generate the largest single eigenvalue & its eigenvectors Simplest method – does not compute matrix decomposition à suitable for large, sparse matrices Inverse Iteration Variation of power iteration method – generates the smallest eigenvalue from the inverse matrix Rayleigh Method http://en.wikipedia.org/wiki/Rayleigh's_method_of_dimensional_analysis Variation of power iteration method Rayleigh Quotient Method Variation of inverse iteration method Matrix Tri-diagonalization Method Use householder algorithm to reduce an NxN symmetric matrix to a tridiagonal real symmetric matrix vua N-2 orthogonal transforms     Whats Next Outside of Numerical Methods there are lots of different types of algorithms that I’ve learned over the decades: Data Mining – (I covered this briefly in a previous post: http://geekswithblogs.net/JoshReuben/archive/2007/12/31/ssas-dm-algorithms.aspx ) Search & Sort Routing Problem Solving Logical Theorem Proving Planning Probabilistic Reasoning Machine Learning Solvers (eg MIP) Bioinformatics (Sequence Alignment, Protein Folding) Quant Finance (I read Wilmott’s books – interesting) Sooner or later, I’ll cover the above topics as well.

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• C#: Adding Functionality to 3rd Party Libraries With Extension Methods

  - by James Michael Hare

  Ever have one of those third party libraries that you love but it's missing that one feature or one piece of syntactical candy that would make it so much more useful?  This, I truly think, is one of the best uses of extension methods.  I began discussing extension methods in my last post (which you find here) where I expounded upon what I thought were some rules of thumb for using extension methods correctly.  As long as you keep in line with those (or similar) rules, they can often be useful for adding that little extra functionality or syntactical simplification for a library that you have little or no control over. Oh sure, you could take an open source project, download the source and add the methods you want, but then every time the library is updated you have to re-add your changes, which can be cumbersome and error prone.  And yes, you could possibly extend a class in a third party library and override features, but that's only if the class is not sealed, static, or constructed via factories. This is the perfect place to use an extension method!  And the best part is, you and your development team don't need to change anything!  Simply add the using for the namespace the extensions are in! So let's consider this example.  I love log4net!  Of all the logging libraries I've played with, it, to me, is one of the most flexible and configurable logging libraries and it performs great.  But this isn't about log4net, well, not directly.  So why would I want to add functionality?  Well, it's missing one thing I really want in the ILog interface: ability to specify logging level at runtime. For example, let's say I declare my ILog instance like so:     using log4net;     public class LoggingTest     {         private static readonly ILog _log = LogManager.GetLogger(typeof(LoggingTest));         ...     }     If you don't know log4net, the details aren't important, just to show that the field _log is the logger I have gotten from log4net. So now that I have that, I can log to it like so:     _log.Debug("This is the lowest level of logging and just for debugging output.");     _log.Info("This is an informational message.  Usual normal operation events.");     _log.Warn("This is a warning, something suspect but not necessarily wrong.");     _log.Error("This is an error, some sort of processing problem has happened.");     _log.Fatal("Fatals usually indicate the program is dying hideously."); And there's many flavors of each of these to log using string formatting, to log exceptions, etc.  But one thing there isn't: the ability to easily choose the logging level at runtime.  Notice, the logging levels above are chosen at compile time.  Of course, you could do some fun stuff with lambdas and wrap it, but that would obscure the simplicity of the interface.  And yes there is a Logger property you can dive down into where you can specify a Level, but the Level properties don't really match the ILog interface exactly and then you have to manually build a LogEvent and... well, it gets messy.  I want something simple and sexy so I can say:     _log.Log(someLevel, "This will be logged at whatever level I choose at runtime!");     Now, some purists out there might say you should always know what level you want to log at, and for the most part I agree with them.  For the most party the ILog interface satisfies 99% of my needs.  In fact, for most application logging yes you do always know the level you will be logging at, but when writing a utility class, you may not always know what level your user wants. I'll tell you, one of my favorite things is to write reusable components.  If I had my druthers I'd write framework libraries and shared components all day!  And being able to easily log at a runtime-chosen level is a big need for me.  After all, if I want my code to really be re-usable, I shouldn't force a user to deal with the logging level I choose. One of my favorite uses for this is in Interceptors -- I'll describe Interceptors in my next post and some of my favorites -- for now just know that an Interceptor wraps a class and allows you to add functionality to an existing method without changing it's signature.  At the risk of over-simplifying, it's a very generic implementation of the Decorator design pattern. So, say for example that you were writing an Interceptor that would time method calls and emit a log message if the method call execution time took beyond a certain threshold of time.  For instance, maybe if your database calls take more than 5,000 ms, you want to log a warning.  Or if a web method call takes over 1,000 ms, you want to log an informational message.  This would be an excellent use of logging at a generic level. So here was my personal wish-list of requirements for my task: Be able to determine if a runtime-specified logging level is enabled. Be able to log generically at a runtime-specified logging level. Have the same look-and-feel of the existing Debug, Info, Warn, Error, and Fatal calls.    Having the ability to also determine if logging for a level is on at runtime is also important so you don't spend time building a potentially expensive logging message if that level is off.  Consider an Interceptor that may log parameters on entrance to the method.  If you choose to log those parameter at DEBUG level and if DEBUG is not on, you don't want to spend the time serializing those parameters. Now, mine may not be the most elegant solution, but it performs really well since the enum I provide all uses contiguous values -- while it's never guaranteed, contiguous switch values usually get compiled into a jump table in IL which is VERY performant - O(1) - but even if it doesn't, it's still so fast you'd never need to worry about it. So first, I need a way to let users pass in logging levels.  Sure, log4net has a Level class, but it's a class with static members and plus it provides way too many options compared to ILog interface itself -- and wouldn't perform as well in my level-check -- so I define an enum like below.     namespace Shared.Logging.Extensions     {         // enum to specify available logging levels.         public enum LoggingLevel         {             Debug,             Informational,             Warning,             Error,             Fatal         }     } Now, once I have this, writing the extension methods I need is trivial.  Once again, I would typically /// comment fully, but I'm eliminating for blogging brevity:     namespace Shared.Logging.Extensions     {         // the extension methods to add functionality to the ILog interface         public static class LogExtensions         {             // Determines if logging is enabled at a given level.             public static bool IsLogEnabled(this ILog logger, LoggingLevel level)             {                 switch (level)                 {                     case LoggingLevel.Debug:                         return logger.IsDebugEnabled;                     case LoggingLevel.Informational:                         return logger.IsInfoEnabled;                     case LoggingLevel.Warning:                         return logger.IsWarnEnabled;                     case LoggingLevel.Error:                         return logger.IsErrorEnabled;                     case LoggingLevel.Fatal:                         return logger.IsFatalEnabled;                 }                                 return false;             }             // Logs a simple message - uses same signature except adds LoggingLevel             public static void Log(this ILog logger, LoggingLevel level, object message)             {                 switch (level)                 {                     case LoggingLevel.Debug:                         logger.Debug(message);                         break;                     case LoggingLevel.Informational:                         logger.Info(message);                         break;                     case LoggingLevel.Warning:                         logger.Warn(message);                         break;                     case LoggingLevel.Error:                         logger.Error(message);                         break;                     case LoggingLevel.Fatal:                         logger.Fatal(message);                         break;                 }             }             // Logs a message and exception to the log at specified level.             public static void Log(this ILog logger, LoggingLevel level, object message, Exception exception)             {                 switch (level)                 {                     case LoggingLevel.Debug:                         logger.Debug(message, exception);                         break;                     case LoggingLevel.Informational:                         logger.Info(message, exception);                         break;                     case LoggingLevel.Warning:                         logger.Warn(message, exception);                         break;                     case LoggingLevel.Error:                         logger.Error(message, exception);                         break;                     case LoggingLevel.Fatal:                         logger.Fatal(message, exception);                         break;                 }             }             // Logs a formatted message to the log at the specified level.              public static void LogFormat(this ILog logger, LoggingLevel level, string format,                                          params object[] args)             {                 switch (level)                 {                     case LoggingLevel.Debug:                         logger.DebugFormat(format, args);                         break;                     case LoggingLevel.Informational:                         logger.InfoFormat(format, args);                         break;                     case LoggingLevel.Warning:                         logger.WarnFormat(format, args);                         break;                     case LoggingLevel.Error:                         logger.ErrorFormat(format, args);                         break;                     case LoggingLevel.Fatal:                         logger.FatalFormat(format, args);                         break;                 }             }         }     } So there it is!  I didn't have to modify the log4net source code, so if a new version comes out, i can just add the new assembly with no changes.  I didn't have to subclass and worry about developers not calling my sub-class instead of the original.  I simply provide the extension methods and it's as if the long lost extension methods were always a part of the ILog interface! Consider a very contrived example using the original interface:     // using the original ILog interface     public class DatabaseUtility     {         private static readonly ILog _log = LogManager.Create(typeof(DatabaseUtility));                 // some theoretical method to time         IDataReader Execute(string statement)         {             var timer = new System.Diagnostics.Stopwatch();                         // do DB magic                                    // this is hard-coded to warn, if want to change at runtime tough luck!             if (timer.ElapsedMilliseconds > 5000 && _log.IsWarnEnabled)             {                 _log.WarnFormat("Statement {0} took too long to execute.", statement);             }             ...         }     }     Now consider this alternate call where the logging level could be perhaps a property of the class          // using the original ILog interface     public class DatabaseUtility     {         private static readonly ILog _log = LogManager.Create(typeof(DatabaseUtility));                 // allow logging level to be specified by user of class instead         public LoggingLevel ThresholdLogLevel { get; set; }                 // some theoretical method to time         IDataReader Execute(string statement)         {             var timer = new System.Diagnostics.Stopwatch();                         // do DB magic                                    // this is hard-coded to warn, if want to change at runtime tough luck!             if (timer.ElapsedMilliseconds > 5000 && _log.IsLogEnabled(ThresholdLogLevel))             {                 _log.LogFormat(ThresholdLogLevel, "Statement {0} took too long to execute.",                     statement);             }             ...         }     } Next time, I'll show one of my favorite uses for these extension methods in an Interceptor.

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• How can I make a career in Formal Methods programming in USA?

  - by A5al Andy

  I've found that my (USA) professors recoil with a near-disgust when I ask them about how to pursue a career in Formal Methods programming. They say, "Oh, that stuff! That stuff is anal. You don't need that European POS to get a job." I'm sure I'll get a job without it, but Formal Methods interests me so much that I bet I'd like to make a career of it. I'd like to learn about Formal Methods at an American University and then work in that field here. I've found that even professors at more important universities than mine don't seem to welcome Formal Methods. Almost all FM research project webpages are semi-abandoned and moldering. Europe is where the action seems to be for this. Can anyone suggest a plan of attack, and along the way explain the antipathy to Formal Methods in the US? I'm a sophomore at a public university in the South.

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• Creating Asynchronous Methods in EJB 3.1

  - by cindo

  Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} OBE of the Month: Creating Asynchronous Methods in EJB 3.1 This OBE covers creating an EJB 3.1 application that demonstrates the use of the @Asynchronous annotation in an Enterprise Java Bean (EJB) class or specific method. In this tutorial, you will create a Java EE 6 Web Application and add the following components to it - a Stateless Session Bean with two asynchronous methods. You define a Servlet to call the asynchronous methods and to keep track of the invocation and completion times to demonstrate the asynchronous nature of the method calls. The index.jsp will contain a form with a submit button, Run allowing you to execute the application. The form will submit to the Servlet which invokes the asynchronous methods defined in the session bean and the response is re-directed to response.jsp. Information about the asynchronous handling procedure is displayed to users. From this information, users will notice that the invoker thread and the called asynchronous thread are working concurrently. Check out this new OBE on the Oracle Learning Library: Creating Asynchronous Methods in EJB 3.1. This OBE is part of the new EJB 3.1 New Features Series. Related OBE’s that might interest you: Creating a No-Interface View Session Bean and Packaging in a WAR File Creating and Accessing a Session Bean in a  Web Application

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• Manager/Container class vs static class methods

  - by Ben

  Suppose I a have a Widget class that is part of a framework used independently by many applications. I create Widget instances in many situations and their lifetimes vary. In addition to Widget's instance specified methods, I would like to be able to perform the follow class wide operations: Find a single Widget instance based on a unique id Iterate over the list of all Widgets Remove a widget from the set of all widgets In order support these operations, I have been considering two approaches: Container class - Create some container or manager class, WidgetContainer, which holds a list of all Widget instances, support iteration and provides methods for Widget addition, removal and lookup. For example in C#: public class WidgetContainer : IEnumerable<Widget { public void AddWidget(Widget); public Widget GetWidget(WidgetId id); public void RemoveWidget(WidgetId id); } Static class methods - Add static class methods to Widget. For example: public class Widget { public Widget(WidgetId id); public static Widget GetWidget(WidgetId id); public static void RemoveWidget(WidgetId id); public static IEnumerable<Widget AllWidgets(); } Using a container class has the added problem of how to access the container class. Make it a singleton?..yuck! Create some World object that provides access to all such container classes? I have seen many frameworks that use the container class approach, so what is the general consensus?

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• SOA Starting Point: Methods for Service Identification and Definition

  As more and more companies start to incorporate a Service Oriented Architectural design approach into their existing enterprise systems, it creates the need for a standardized integration technology. One common technology used by companies is an Enterprise Service Bus (ESB). An ESB, as defined by Progress Software, connects and mediates all communications and interactions between services. In essence an ESB is a form of middleware that allows services to communicate with one another regardless of framework, environment, or location. With the emergence of ESB, a new emphasis is now being placed on approaches that can be used to determine what Web services should be built. In addition, what order should these services be built? In May 2011, SOA Magazine published an article that identified 10 common methods for identifying and defining services. SOA’s Ten Common Methods for Service Identification and Definition: Business Process Decomposition Business Functions Business Entity Objects Ownership and Responsibility Goal-Driven Component-Based Existing Supply (Bottom-Up) Front-Office Application Usage Analysis Infrastructure Non-Functional Requirements  Each of these methods provides various pros and cons in regards to their use within the design process. I personally feel that during a design process, multiple methodologies should be used in order to accurately define a design for a system or enterprise system. Personally, I like to create a custom cocktail derived from combining these methodologies in order to ensure that my design fits with the project’s and business’s needs while still following development standards and guidelines. Of these ten methods, I am particularly fond of Business Process Decomposition, Business Functions, Goal-Driven, Component-Based, and routinely use them in my designs.  Works Cited Hubbers, J.-W., Ligthart, A., & Terlouw , L. (2007, 12 10). Ten Ways to Identify Services. Retrieved from SOA Magazine: http://www.soamag.com/I13/1207-1.php Progress.com. (2011, 10 30). ESB ARCHITECTURE AND LIFECYCLE DEFINITION. Retrieved from Progress.com: http://web.progress.com/en/esb-architecture-lifecycle-definition.html

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• Inside the DLR – Invoking methods

  - by Simon Cooper

  So, we’ve looked at how a dynamic call is represented in a compiled assembly, and how the dynamic lookup is performed at runtime. The last piece of the puzzle is how the resolved method gets invoked, and that is the subject of this post. Invoking methods As discussed in my previous posts, doing a full lookup and bind at runtime each and every single time the callsite gets invoked would be far too slow to be usable. The results obtained from the callsite binder must to be cached, along with a series of conditions to determine whether the cached result can be reused. So, firstly, how are the conditions represented? These conditions can be anything; they are determined entirely by the semantics of the language the binder is representing. The binder has to be able to return arbitary code that is then executed to determine whether the conditions apply or not. Fortunately, .NET 4 has a neat way of representing arbitary code that can be easily combined with other code – expression trees. All the callsite binder has to return is an expression (called a ‘restriction’) that evaluates to a boolean, returning true when the restriction passes (indicating the corresponding method invocation can be used) and false when it does’t. If the bind result is also represented in an expression tree, these can be combined easily like so: if ([restriction is true]) { [invoke cached method] } Take my example from my previous post: public class ClassA { public static void TestDynamic() { CallDynamic(new ClassA(), 10); CallDynamic(new ClassA(), "foo"); } public static void CallDynamic(dynamic d, object o) { d.Method(o); } public void Method(int i) {} public void Method(string s) {} } When the Method(int) method is first bound, along with an expression representing the result of the bind lookup, the C# binder will return the restrictions under which that bind can be reused. In this case, it can be reused if the types of the parameters are the same: if (thisArg.GetType() == typeof(ClassA) && arg1.GetType() == typeof(int)) { thisClassA.Method(i); } Caching callsite results So, now, it’s up to the callsite to link these expressions returned from the binder together in such a way that it can determine which one from the many it has cached it should use. This caching logic is all located in the System.Dynamic.UpdateDelegates class. It’ll help if you’ve got this type open in a decompiler to have a look yourself. For each callsite, there are 3 layers of caching involved: The last method invoked on the callsite. All methods that have ever been invoked on the callsite. All methods that have ever been invoked on any callsite of the same type. We’ll cover each of these layers in order Level 1 cache: the last method called on the callsite When a CallSite<T> object is first instantiated, the Target delegate field (containing the delegate that is called when the callsite is invoked) is set to one of the UpdateAndExecute generic methods in UpdateDelegates, corresponding to the number of parameters to the callsite, and the existance of any return value. These methods contain most of the caching, invoke, and binding logic for the callsite. The first time this method is invoked, the UpdateAndExecute method finds there aren’t any entries in the caches to reuse, and invokes the binder to resolve a new method. Once the callsite has the result from the binder, along with any restrictions, it stitches some extra expressions in, and replaces the Target field in the callsite with a compiled expression tree similar to this (in this example I’m assuming there’s no return value): if ([restriction is true]) { [invoke cached method] return; } if (callSite._match) { _match = false; return; } else { UpdateAndExecute(callSite, arg0, arg1, ...); } Woah. What’s going on here? Well, this resulting expression tree is actually the first level of caching. The Target field in the callsite, which contains the delegate to call when the callsite is invoked, is set to the above code compiled from the expression tree into IL, and then into native code by the JIT. This code checks whether the restrictions of the last method that was invoked on the callsite (the ‘primary’ method) match, and if so, executes that method straight away. This means that, the next time the callsite is invoked, the first code that executes is the restriction check, executing as native code! This makes this restriction check on the primary cached delegate very fast. But what if the restrictions don’t match? In that case, the second part of the stitched expression tree is executed. What this section should be doing is calling back into the UpdateAndExecute method again to resolve a new method. But it’s slightly more complicated than that. To understand why, we need to understand the second and third level caches. Level 2 cache: all methods that have ever been invoked on the callsite When a binder has returned the result of a lookup, as well as updating the Target field with a compiled expression tree, stitched together as above, the callsite puts the same compiled expression tree in an internal list of delegates, called the rules list. This list acts as the level 2 cache. Why use the same delegate? Stitching together expression trees is an expensive operation. You don’t want to do it every time the callsite is invoked. Ideally, you would create one expression tree from the binder’s result, compile it, and then use the resulting delegate everywhere in the callsite. But, if the same delegate is used to invoke the callsite in the first place, and in the caches, that means each delegate needs two modes of operation. An ‘invoke’ mode, for when the delegate is set as the value of the Target field, and a ‘match’ mode, used when UpdateAndExecute is searching for a method in the callsite’s cache. Only in the invoke mode would the delegate call back into UpdateAndExecute. In match mode, it would simply return without doing anything. This mode is controlled by the _match field in CallSite<T>. The first time the callsite is invoked, _match is false, and so the Target delegate is called in invoke mode. Then, if the initial restriction check fails, the Target delegate calls back into UpdateAndExecute. This method sets _match to true, then calls all the cached delegates in the rules list in match mode to try and find one that passes its restrictions, and invokes it. However, there needs to be some way for each cached delegate to inform UpdateAndExecute whether it passed its restrictions or not. To do this, as you can see above, it simply re-uses _match, and sets it to false if it did not pass the restrictions. This allows the code within each UpdateAndExecute method to check for cache matches like so: foreach (T cachedDelegate in Rules) { callSite._match = true; cachedDelegate(); // sets _match to false if restrictions do not pass if (callSite._match) { // passed restrictions, and the cached method was invoked // set this delegate as the primary target to invoke next time callSite.Target = cachedDelegate; return; } // no luck, try the next one... } Level 3 cache: all methods that have ever been invoked on any callsite with the same signature The reason for this cache should be clear – if a method has been invoked through a callsite in one place, then it is likely to be invoked on other callsites in the codebase with the same signature. Rather than living in the callsite, the ‘global’ cache for callsite delegates lives in the CallSiteBinder class, in the Cache field. This is a dictionary, typed on the callsite delegate signature, providing a RuleCache<T> instance for each delegate signature. This is accessed in the same way as the level 2 callsite cache, by the UpdateAndExecute methods. When a method is matched in the global cache, it is copied into the callsite and Target cache before being executed. Putting it all together So, how does this all fit together? Like so (I’ve omitted some implementation & performance details): That, in essence, is how the DLR performs its dynamic calls nearly as fast as statically compiled IL code. Extensive use of expression trees, compiled to IL and then into native code. Multiple levels of caching, the first of which executes immediately when the dynamic callsite is invoked. And a clever re-use of compiled expression trees that can be used in completely different contexts without being recompiled. All in all, a very fast and very clever reflection caching mechanism.

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• Breaking up classes and methods into smaller units

  - by micahhoover

  During code reviews a couple devs have recommended I break up my methods into smaller methods. Their justification was (1) increased readability and (2) the back trace that comes back from production showing the method name is more specific to the line of code that failed. There may have also been some colorful words about functional programming. Additionally I think I may have failed an interview a while back because I didn't give an acceptable answer about when to break things up. My inclination is that when I see a bunch of methods in a class or across a bunch of files, it isn't clear to me how they flow together, and how many times each one gets called. I don't really have a good feel for the linearity of it as quickly just by eye-balling it. The other thing is a lot of people seem to place a premium of organization over content (e.g. 'Look at how organized my sock drawer is!' Me: 'Overall, I think I can get to my socks faster if you count the time it took to organize them'). Our business requirements are not very stable. I'm afraid that if the classes/methods are very granular it will take longer to refactor to requirement changes. I'm not sure how much of a factor this should be. Anyway, computer science is part art / part science, but I'm not sure how much this applies to this issue.

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• Should we rename overloaded methods?

  - by Mik378

  Assume an interface containing these methods : Car find(long id); List<Car> find(String model); Is it better to rename them like this? Car findById(long id); List findByModel(String model); Indeed, any developer who use this API won't need to look at the interface for knowing possible arguments of initial find() methods. So my question is more general : What is the benefit of using overloaded methods in code since it reduce readability?

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• Configuring Fed Authentication Methods in OIF / IdP

  - by Damien Carru

  In this article, I will provide examples on how to configure OIF/IdP to map OAM Authentication Schemes to Federation Authentication Methods, based on the concepts introduced in my previous entry. I will show examples for the three protocols supported by OIF: SAML 2.0 SSO SAML 1.1 SSO OpenID 2.0 Enjoy the reading! Configuration As I mentioned in my previous article, mapping Federation Authentication Methods to OAM Authentication Schemes is protocol dependent, since the methods are defined in the various protocols (SAML 2.0, SAML 1.1, OpenID 2.0). As such, the WLST commands to set those mappings will involve: Either the SP Partner Profile and affect all Partners referencing that profile, which do not override the Federation Authentication Method to OAM Authentication Scheme mappings Or the SP Partner entry, which will only affect the SP Partner It is important to note that if an SP Partner is configured to define one or more Federation Authentication Method to OAM Authentication Scheme mappings, then all the mappings defined in the SP Partner Profile will be ignored. WLST Commands The two OIF WLST commands that can be used to define mapping Federation Authentication Methods to OAM Authentication Schemes are: addSPPartnerProfileAuthnMethod() to define a mapping on an SP Partner Profile, taking as parameters: The name of the SP Partner Profile The Federation Authentication Method The OAM Authentication Scheme name addSPPartnerAuthnMethod() to define a mapping on an SP Partner , taking as parameters: The name of the SP Partner The Federation Authentication Method The OAM Authentication Scheme name Note: I will discuss in a subsequent article the other parameters of those commands. In the next sections, I will show examples on how to use those methods: For SAML 2.0, I will configure the SP Partner Profile, that will apply all the mappings to SP Partners referencing this profile, unless they override mapping definition For SAML 1.1, I will configure the SP Partner. For OpenID 2.0, I will configure the SP/RP Partner SAML 2.0 Test Setup In this setup, OIF is acting as an IdP and is integrated with a remote SAML 2.0 SP partner identified by AcmeSP. In this test, I will perform Federation SSO with OIF/IdP configured to: Use LDAPScheme as the Authentication Scheme Use BasicScheme as the Authentication Scheme Map BasicSessionScheme  to  the urn:oasis:names:tc:SAML:2.0:ac:classes:Password Federation Authentication Method Use OAMLDAPPluginAuthnScheme as the Authentication Scheme Map OAMLDAPPluginAuthnScheme to  the urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport Federation Authentication Method LDAPScheme as Authentication Scheme Using the OOTB settings regarding user authentication in OAM, the user will be challenged via a FORM based login page based on the LDAPScheme. Also the default Federation Authentication Method mappings configuration maps only the urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport to LDAPScheme (also marked as the default scheme used for authentication), FAAuthScheme, BasicScheme and BasicFAScheme. After authentication via FORM, OIF/IdP would issue an Assertion similar to: <samlp:Response ...>    <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>    <samlp:Status>        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>    </samlp:Status>    <saml:Assertion ...>        <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>        <dsig:Signature>            ...        </dsig:Signature>        <saml:Subject>            <saml:NameID ...>[email protected]</saml:NameID>            <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">                <saml:SubjectConfirmationData .../>            </saml:SubjectConfirmation>        </saml:Subject>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthnInstant="2014-03-21T20:53:55Z" SessionIndex="id-6i-Dm0yB-HekG6cejktwcKIFMzYE8Yrmqwfd0azz" SessionNotOnOrAfter="2014-03-21T21:53:55Z">            <saml:AuthnContext>                <saml:AuthnContextClassRef>                   urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport                </saml:AuthnContextClassRef>            </saml:AuthnContext>        </saml:AuthnStatement>    </saml:Assertion></samlp:Response> BasicScheme as Authentication Scheme For this test, I will switch the default Authentication Scheme for the SP Partner Profile to BasicScheme instead of LDAPScheme. I will use the OIF WLST setSPPartnerProfileDefaultScheme() command and specify which scheme to be used as the default for the SP Partner Profile referenced by AcmeSP (which is saml20-sp-partner-profile in this case: getFedPartnerProfile("AcmeSP", "sp") ): Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the setSPPartnerProfileDefaultScheme() command:setSPPartnerProfileDefaultScheme("saml20-sp-partner-profile", "BasicScheme") Exit the WLST environment:exit() The user will now be challenged via HTTP Basic Authentication defined in the BasicScheme for AcmeSP. Also, as noted earlier, the default Federation Authentication Method mappings configuration maps only the urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport to LDAPScheme (also marked as the default scheme used for authentication), FAAuthScheme, BasicScheme and BasicFAScheme. After authentication via HTTP Basic Authentication, OIF/IdP would issue an Assertion similar to: <samlp:Response ...>    <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>    <samlp:Status>        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>    </samlp:Status>    <saml:Assertion ...>        <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>        <dsig:Signature>            ...        </dsig:Signature>        <saml:Subject>            <saml:NameID ...>[email protected]</saml:NameID>            <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">                <saml:SubjectConfirmationData .../>            </saml:SubjectConfirmation>        </saml:Subject>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthnInstant="2014-03-21T20:53:55Z" SessionIndex="id-6i-Dm0yB-HekG6cejktwcKIFMzYE8Yrmqwfd0azz" SessionNotOnOrAfter="2014-03-21T21:53:55Z">            <saml:AuthnContext>                <saml:AuthnContextClassRef>                   urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport                </saml:AuthnContextClassRef>            </saml:AuthnContext>        </saml:AuthnStatement>    </saml:Assertion></samlp:Response> Mapping BasicScheme To change the Federation Authentication Method mapping for the BasicScheme to urn:oasis:names:tc:SAML:2.0:ac:classes:Password instead of urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport for the saml20-sp-partner-profile SAML 2.0 SP Partner Profile (the profile to which my AcmeSP Partner is bound to), I will execute the addSPPartnerProfileAuthnMethod() method: Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the addSPPartnerProfileAuthnMethod() command:addSPPartnerProfileAuthnMethod("saml20-sp-partner-profile", "urn:oasis:names:tc:SAML:2.0:ac:classes:Password", "BasicScheme") Exit the WLST environment:exit() After authentication via HTTP Basic Authentication, OIF/IdP would now issue an Assertion similar to (see that the AuthnContextClassRef was changed from PasswordProtectedTransport to Password): <samlp:Response ...>    <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>    <samlp:Status>        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>    </samlp:Status>    <saml:Assertion ...>        <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>        <dsig:Signature>            ...        </dsig:Signature>        <saml:Subject>            <saml:NameID ...>[email protected]</saml:NameID>            <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">                <saml:SubjectConfirmationData .../>            </saml:SubjectConfirmation>        </saml:Subject>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthnInstant="2014-03-21T20:53:55Z" SessionIndex="id-6i-Dm0yB-HekG6cejktwcKIFMzYE8Yrmqwfd0azz" SessionNotOnOrAfter="2014-03-21T21:53:55Z">            <saml:AuthnContext>                <saml:AuthnContextClassRef>                   urn:oasis:names:tc:SAML:2.0:ac:classes:Password                </saml:AuthnContextClassRef>            </saml:AuthnContext>        </saml:AuthnStatement>    </saml:Assertion></samlp:Response> OAMLDAPPluginAuthnScheme as Authentication Scheme For this test, I will switch the default Authentication Scheme for the SP Partner Profile to OAMLDAPPluginAuthnScheme instead of BasicScheme. I will use the OIF WLST setSPPartnerProfileDefaultScheme() command and specify which scheme to be used as the default for the SP Partner Profile referenced by AcmeSP (which is saml20-sp-partner-profile in this case: getFedPartnerProfile("AcmeSP", "sp") ): Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the setSPPartnerProfileDefaultScheme() command:setSPPartnerProfileDefaultScheme("saml20-sp-partner-profile", "OAMLDAPPluginAuthnScheme") Exit the WLST environment:exit() The user will now be challenged via FORM defined in the OAMLDAPPluginAuthnScheme for AcmeSP. Contrarily to LDAPScheme and BasicScheme, the OAMLDAPPluginAuthnScheme is not mapped by default to any Federation Authentication Methods. As such, OIF/IdP will not be able to find a Federation Authentication Method and will set the method in the SAML Assertion to the OAM Authentication Scheme name. After authentication via FORM, OIF/IdP would issue an Assertion similar to (see the AuthnContextClassRef set to OAMLDAPPluginAuthnScheme): <samlp:Response ...>    <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>    <samlp:Status>        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>    </samlp:Status>    <saml:Assertion ...>        <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>        <dsig:Signature>            ...        </dsig:Signature>        <saml:Subject>            <saml:NameID ...>[email protected]</saml:NameID>            <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">                <saml:SubjectConfirmationData .../>            </saml:SubjectConfirmation>        </saml:Subject>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthnInstant="2014-03-21T20:53:55Z" SessionIndex="id-6i-Dm0yB-HekG6cejktwcKIFMzYE8Yrmqwfd0azz" SessionNotOnOrAfter="2014-03-21T21:53:55Z">            <saml:AuthnContext>                <saml:AuthnContextClassRef> OAMLDAPPluginAuthnScheme                </saml:AuthnContextClassRef>            </saml:AuthnContext>        </saml:AuthnStatement>    </saml:Assertion></samlp:Response> Mapping OAMLDAPPluginAuthnScheme To add the OAMLDAPPluginAuthnScheme  to the Federation Authentication Method urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport mapping, I will execute the addSPPartnerProfileAuthnMethod() method: Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the addSPPartnerProfileAuthnMethod() command:addSPPartnerProfileAuthnMethod("saml20-sp-partner-profile", "urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport", "OAMLDAPPluginAuthnScheme") Exit the WLST environment:exit() After authentication via FORM, OIF/IdP would now issue an Assertion similar to (see that the method was changed from OAMLDAPPluginAuthnScheme to PasswordProtectedTransport): <samlp:Response ...>    <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>    <samlp:Status>        <samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>    </samlp:Status>    <saml:Assertion ...>        <saml:Issuer ...>https://idp.com/oam/fed</saml:Issuer>        <dsig:Signature>            ...        </dsig:Signature>        <saml:Subject>            <saml:NameID ...>[email protected]</saml:NameID>            <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">                <saml:SubjectConfirmationData .../>            </saml:SubjectConfirmation>        </saml:Subject>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthnInstant="2014-03-21T20:53:55Z" SessionIndex="id-6i-Dm0yB-HekG6cejktwcKIFMzYE8Yrmqwfd0azz" SessionNotOnOrAfter="2014-03-21T21:53:55Z">            <saml:AuthnContext>                <saml:AuthnContextClassRef>                   urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport                </saml:AuthnContextClassRef>            </saml:AuthnContext>        </saml:AuthnStatement>    </saml:Assertion></samlp:Response> SAML 1.1 Test Setup In this setup, OIF is acting as an IdP and is integrated with a remote SAML 1.1 SP partner identified by AcmeSP. In this test, I will perform Federation SSO with OIF/IdP configured to: Use LDAPScheme as the Authentication Scheme Use OAMLDAPPluginAuthnScheme as the Authentication Scheme Map OAMLDAPPluginAuthnScheme to  the urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport Federation Authentication Method Use LDAPScheme as the Authentication Scheme Map LDAPScheme to  the urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport Federation Authentication Method LDAPScheme as Authentication Scheme Using the OOTB settings regarding user authentication in OAM, the user will be challenged via a FORM based login page based on the LDAPScheme. Also the default Federation Authentication Method mappings configuration maps only the urn:oasis:names:tc:SAML:1.0:am:password to LDAPScheme (also marked as the default scheme used for authentication), FAAuthScheme, BasicScheme and BasicFAScheme. After authentication via FORM, OIF/IdP would issue an Assertion similar to: <samlp:Response ...>    <samlp:Status>        <samlp:StatusCode Value="samlp:Success"/>    </samlp:Status>    <saml:Assertion Issuer="https://idp.com/oam/fed" ...>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp/ssov11</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthenticationInstant="2014-03-21T20:53:55Z" AuthenticationMethod="urn:oasis:names:tc:SAML:1.0:am:password">            <saml:Subject>                <saml:NameIdentifier ...>[email protected]</saml:NameIdentifier>                <saml:SubjectConfirmation>                   <saml:ConfirmationMethod>                       urn:oasis:names:tc:SAML:1.0:cm:bearer                   </saml:ConfirmationMethod>                </saml:SubjectConfirmation>            </saml:Subject>        </saml:AuthnStatement>        <dsig:Signature>            ...        </dsig:Signature>    </saml:Assertion></samlp:Response> OAMLDAPPluginAuthnScheme as Authentication Scheme For this test, I will switch the default Authentication Scheme for the SP Partner to OAMLDAPPluginAuthnScheme instead of LDAPScheme. I will use the OIF WLST setSPPartnerDefaultScheme() command and specify which scheme to be used as the default for the SP Partner: Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the setSPPartnerDefaultScheme() command:setSPPartnerDefaultScheme("AcmeSP", "OAMLDAPPluginAuthnScheme") Exit the WLST environment:exit() The user will be challenged via FORM defined in the OAMLDAPPluginAuthnScheme for AcmeSP. Contrarily to LDAPScheme, the OAMLDAPPluginAuthnScheme is not mapped by default to any Federation Authentication Methods (in the SP Partner Profile). As such, OIF/IdP will not be able to find a Federation Authentication Method and will set the method in the SAML Assertion to the OAM Authentication Scheme name. After authentication via FORM, OIF/IdP would issue an Assertion similar to (see the AuthenticationMethod set to OAMLDAPPluginAuthnScheme): <samlp:Response ...>    <samlp:Status>        <samlp:StatusCode Value="samlp:Success"/>    </samlp:Status>    <saml:Assertion Issuer="https://idp.com/oam/fed" ...>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp/ssov11</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthenticationInstant="2014-03-21T20:53:55Z" AuthenticationMethod="OAMLDAPPluginAuthnScheme">            <saml:Subject>                <saml:NameIdentifier ...>[email protected]</saml:NameIdentifier>                <saml:SubjectConfirmation>                   <saml:ConfirmationMethod>                       urn:oasis:names:tc:SAML:1.0:cm:bearer                   </saml:ConfirmationMethod>                </saml:SubjectConfirmation>            </saml:Subject>        </saml:AuthnStatement>        <dsig:Signature>            ...        </dsig:Signature>    </saml:Assertion></samlp:Response> Mapping OAMLDAPPluginAuthnScheme To map the OAMLDAPPluginAuthnScheme  to the Federation Authentication Method urn:oasis:names:tc:SAML:1.0:am:password for this SP Partner only, I will execute the addSPPartnerAuthnMethod() method: Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the addSPPartnerAuthnMethod() command:addSPPartnerAuthnMethod("AcmeSP", "urn:oasis:names:tc:SAML:1.0:am:password", "OAMLDAPPluginAuthnScheme") Exit the WLST environment:exit() After authentication via FORM, OIF/IdP would now issue an Assertion similar to (see that the method was changed from OAMLDAPPluginAuthnScheme to password): <samlp:Response ...>    <samlp:Status>        <samlp:StatusCode Value="samlp:Success"/>    </samlp:Status>    <saml:Assertion Issuer="https://idp.com/oam/fed" ...>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp/ssov11</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthenticationInstant="2014-03-21T20:53:55Z" AuthenticationMethod="urn:oasis:names:tc:SAML:1.0:am:password">            <saml:Subject>                <saml:NameIdentifier ...>[email protected]</saml:NameIdentifier>                <saml:SubjectConfirmation>                   <saml:ConfirmationMethod>                       urn:oasis:names:tc:SAML:1.0:cm:bearer                   </saml:ConfirmationMethod>                </saml:SubjectConfirmation>            </saml:Subject>        </saml:AuthnStatement>        <dsig:Signature>            ...        </dsig:Signature>    </saml:Assertion></samlp:Response> LDAPScheme as Authentication Scheme I will now show that by defining a Federation Authentication Mapping at the Partner level, this now ignores all mappings defined at the SP Partner Profile level. For this test, I will switch the default Authentication Scheme for this SP Partner back to LDAPScheme, and the Assertion issued by OIF/IdP will not be able to map this LDAPScheme to a Federation Authentication Method anymore, since A Federation Authentication Method mapping is defined at the SP Partner level and thus the mappings defined at the SP Partner Profile are ignored The LDAPScheme is not listed in the mapping at the Partner level I will use the OIF WLST setSPPartnerDefaultScheme() command and specify which scheme to be used as the default for this SP Partner: Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the setSPPartnerDefaultScheme() command:setSPPartnerDefaultScheme("AcmeSP", "LDAPScheme") Exit the WLST environment:exit() After authentication via FORM, OIF/IdP would issue an Assertion similar to (see the AuthenticationMethod set to LDAPScheme): <samlp:Response ...>    <samlp:Status>        <samlp:StatusCode Value="samlp:Success"/>    </samlp:Status>    <saml:Assertion Issuer="https://idp.com/oam/fed" ...>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp/ssov11</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthenticationInstant="2014-03-21T20:53:55Z" AuthenticationMethod="LDAPScheme">            <saml:Subject>                <saml:NameIdentifier ...>[email protected]</saml:NameIdentifier>                <saml:SubjectConfirmation>                   <saml:ConfirmationMethod>                       urn:oasis:names:tc:SAML:1.0:cm:bearer                   </saml:ConfirmationMethod>                </saml:SubjectConfirmation>            </saml:Subject>        </saml:AuthnStatement>        <dsig:Signature>            ...        </dsig:Signature>    </saml:Assertion></samlp:Response> Mapping LDAPScheme at Partner Level To fix this issue, we will need to add the LDAPScheme  to the Federation Authentication Method urn:oasis:names:tc:SAML:1.0:am:password mapping for this SP Partner only. I will execute the addSPPartnerAuthnMethod() method: Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the addSPPartnerAuthnMethod() command:addSPPartnerAuthnMethod("AcmeSP", "urn:oasis:names:tc:SAML:1.0:am:password", "LDAPScheme") Exit the WLST environment:exit() After authentication via FORM, OIF/IdP would now issue an Assertion similar to (see that the method was changed from LDAPScheme to password): <samlp:Response ...>    <samlp:Status>        <samlp:StatusCode Value="samlp:Success"/>    </samlp:Status>    <saml:Assertion Issuer="https://idp.com/oam/fed" ...>        <saml:Conditions ...>            <saml:AudienceRestriction>                <saml:Audience>https://acme.com/sp/ssov11</saml:Audience>            </saml:AudienceRestriction>        </saml:Conditions>        <saml:AuthnStatement AuthenticationInstant="2014-03-21T20:53:55Z" AuthenticationMethod="urn:oasis:names:tc:SAML:1.0:am:password">            <saml:Subject>                <saml:NameIdentifier ...>[email protected]</saml:NameIdentifier>                <saml:SubjectConfirmation>                   <saml:ConfirmationMethod>                       urn:oasis:names:tc:SAML:1.0:cm:bearer                   </saml:ConfirmationMethod>                </saml:SubjectConfirmation>            </saml:Subject>        </saml:AuthnStatement>        <dsig:Signature>            ...        </dsig:Signature>    </saml:Assertion></samlp:Response> OpenID 2.0 In the OpenID 2.0 flows, the RP must request use of PAPE, in order for OIF/IdP/OP to include PAPE information. For OpenID 2.0, the configuration will involve mapping a list of OpenID 2.0 policies to a list of Authentication Schemes. The WLST command will take a list of policies, delimited by the ',' character, instead of SAML 2.0 or SAML 1.1 where a single Federation Authentication Method had to be specified. Test Setup In this setup, OIF is acting as an IdP/OP and is integrated with a remote OpenID 2.0 SP/RP partner identified by AcmeRP. In this test, I will perform Federation SSO with OIF/IdP configured to: Use LDAPScheme as the Authentication Scheme Map LDAPScheme to  the http://schemas.openid.net/pape/policies/2007/06/phishing-resistant and http://openid-policies/password-protected policies Federation Authentication Methods (the second one is a custom for this use case) LDAPScheme as Authentication Scheme Using the OOTB settings regarding user authentication in OAM, the user will be challenged via a FORM based login page based on the LDAPScheme. No Federation Authentication Method is defined OOTB for OpenID 2.0, so if the IdP/OP issue an SSO response with a PAPE Response element, it will specify the scheme name instead of Federation Authentication Methods After authentication via FORM, OIF/IdP would issue an SSO Response similar to: https://acme.com/openid?refid=id-9PKVXZmRxAeDYcgLqPm36ClzOMA-&openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0&openid.mode=id_res&openid.op_endpoint=https%3A%2F%2Fidp.com%2Fopenid&openid.claimed_id=https%3A%2F%2Fidp.com%2Fopenid%3Fid%3Did-38iCmmlAVEXPsFjnFVKArfn5RIiF75D5doorhEgqqPM%3D&openid.identity=https%3A%2F%2Fidp.com%2Fopenid%3Fid%3Did-38iCmmlAVEXPsFjnFVKArfn5RIiF75D5doorhEgqqPM%3D&openid.return_to=https%3A%2F%2Facme.com%2Fopenid%3Frefid%3Did-9PKVXZmRxAeDYcgLqPm36ClzOMA-&openid.response_nonce=2014-03-24T19%3A20%3A06Zid-YPa2kTNNFftZkgBb460jxJGblk2g--iNwPpDI7M1&openid.assoc_handle=id-6a5S6zhAKaRwQNUnjTKROREdAGSjWodG1el4xyz3&openid.ns.ax=http%3A%2F%2Fopenid.net%2Fsrv%2Fax%2F1.0&openid.ax.mode=fetch_response&openid.ax.type.attr0=http%3A%2F%2Fsession%2Fcount&openid.ax.value.attr0=1&openid.ax.type.attr1=http%3A%2F%2Fopenid.net%2Fschema%2FnamePerson%2Ffriendly&openid.ax.value.attr1=My+name+is+Bobby+Smith&openid.ax.type.attr2=http%3A%2F%2Fschemas.openid.net%2Fax%2Fapi%2Fuser_id&openid.ax.value.attr2=bob&openid.ax.type.attr3=http%3A%2F%2Faxschema.org%2Fcontact%2Femail&openid.ax.value.attr3=bob%40oracle.com&openid.ax.type.attr4=http%3A%2F%2Fsession%2Fipaddress&openid.ax.value.attr4=10.145.120.253&openid.ns.pape=http%3A%2F%2Fspecs.openid.net%2Fextensions%2Fpape%2F1.0&openid.pape.auth_time=2014-03-24T19%3A20%3A05Z&openid.pape.auth_policies=LDAPScheme&openid.signed=op_endpoint%2Cclaimed_id%2Cidentity%2Creturn_to%2Cresponse_nonce%2Cassoc_handle%2Cns.ax%2Cax.mode%2Cax.type.attr0%2Cax.value.attr0%2Cax.type.attr1%2Cax.value.attr1%2Cax.type.attr2%2Cax.value.attr2%2Cax.type.attr3%2Cax.value.attr3%2Cax.type.attr4%2Cax.value.attr4%2Cns.pape%2Cpape.auth_time%2Cpape.auth_policies&openid.sig=mYMgbGYSs22l8e%2FDom9NRPw15u8%3D Mapping LDAPScheme To map the LDAP Scheme to the http://schemas.openid.net/pape/policies/2007/06/phishing-resistant and http://openid-policies/password-protected policies Federation Authentication Methods, I will execute the addSPPartnerAuthnMethod() method (the policies will be comma separated): Enter the WLST environment by executing:$IAM_ORACLE_HOME/common/bin/wlst.sh Connect to the WLS Admin server:connect() Navigate to the Domain Runtime branch:domainRuntime() Execute the addSPPartnerAuthnMethod() command:addSPPartnerAuthnMethod("AcmeRP", "http://schemas.openid.net/pape/policies/2007/06/phishing-resistant,http://openid-policies/password-protected", "LDAPScheme") Exit the WLST environment:exit() After authentication via FORM, OIF/IdP would now issue an Assertion similar to (see that the method was changed from LDAPScheme to the two policies): https://acme.com/openid?refid=id-9PKVXZmRxAeDYcgLqPm36ClzOMA-&openid.ns=http%3A%2F%2Fspecs.openid.net%2Fauth%2F2.0&openid.mode=id_res&openid.op_endpoint=https%3A%2F%2Fidp.com%2Fopenid&openid.claimed_id=https%3A%2F%2Fidp.com%2Fopenid%3Fid%3Did-38iCmmlAVEXPsFjnFVKArfn5RIiF75D5doorhEgqqPM%3D&openid.identity=https%3A%2F%2Fidp.com%2Fopenid%3Fid%3Did-38iCmmlAVEXPsFjnFVKArfn5RIiF75D5doorhEgqqPM%3D&openid.return_to=https%3A%2F%2Facme.com%2Fopenid%3Frefid%3Did-9PKVXZmRxAeDYcgLqPm36ClzOMA-&openid.response_nonce=2014-03-24T19%3A20%3A06Zid-YPa2kTNNFftZkgBb460jxJGblk2g--iNwPpDI7M1&openid.assoc_handle=id-6a5S6zhAKaRwQNUnjTKROREdAGSjWodG1el4xyz3&openid.ns.ax=http%3A%2F%2Fopenid.net%2Fsrv%2Fax%2F1.0&openid.ax.mode=fetch_response&openid.ax.type.attr0=http%3A%2F%2Fsession%2Fcount&openid.ax.value.attr0=1&openid.ax.type.attr1=http%3A%2F%2Fopenid.net%2Fschema%2FnamePerson%2Ffriendly&openid.ax.value.attr1=My+name+is+Bobby+Smith&openid.ax.type.attr2=http%3A%2F%2Fschemas.openid.net%2Fax%2Fapi%2Fuser_id&openid.ax.value.attr2=bob&openid.ax.type.attr3=http%3A%2F%2Faxschema.org%2Fcontact%2Femail&openid.ax.value.attr3=bob%40oracle.com&openid.ax.type.attr4=http%3A%2F%2Fsession%2Fipaddress&openid.ax.value.attr4=10.145.120.253&openid.ns.pape=http%3A%2F%2Fspecs.openid.net%2Fextensions%2Fpape%2F1.0&openid.pape.auth_time=2014-03-24T19%3A20%3A05Z&openid.pape.auth_policies=http%3A%2F%2Fschemas.openid.net%2Fpape%2Fpolicies%2F2007%2F06%2Fphishing-resistant+http%3A%2F%2Fopenid-policies%2Fpassword-protected&openid.signed=op_endpoint%2Cclaimed_id%2Cidentity%2Creturn_to%2Cresponse_nonce%2Cassoc_handle%2Cns.ax%2Cax.mode%2Cax.type.attr0%2Cax.value.attr0%2Cax.type.attr1%2Cax.value.attr1%2Cax.type.attr2%2Cax.value.attr2%2Cax.type.attr3%2Cax.value.attr3%2Cax.type.attr4%2Cax.value.attr4%2Cns.pape%2Cpape.auth_time%2Cpape.auth_policies&openid.sig=mYMgbGYSs22l8e%2FDom9NRPw15u8%3D In the next article, I will cover how OIF/IdP can be configured so that an SP can request a specific Federation Authentication Method to challenge the user during Federation SSO.Cheers,Damien Carru

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• Strategies for invoking subclass methods on generic objects

  - by Brad Patton

  I've run into this issue in a number of places and have solved it a bunch of different ways but looking for other solutions or opinions on how to address. The scenario is when you have a collection of objects all based off of the same superclass but you want to perform certain actions based only on instances of some of the subclasses. One contrived example of this might be an HTML document made up of elements. You could have a superclass named HTMLELement and subclasses of Headings, Paragraphs, Images, Comments, etc. To invoke a common action across all of the objects you declare a virtual method in the superclass and specific implementations in all of the subclasses. So to render the document you could loop all of the different objects in the document and call a common Render() method on each instance. It's the case where again using the same generic objects in the collection I want to perform different actions for instances of specific subclass (or set of subclasses). For example (an remember this is just an example) when iterating over the collection, elements with external links need to be downloaded (e.g. JS, CSS, images) and some might require additional parsing (JS, CSS). What's the best way to handle those special cases. Some of the strategies I've used or seen used include: Virtual methods in the base class. So in the base class you have a virtual LoadExternalContent() method that does nothing and then override it in the specific subclasses that need to implement it. The benefit being that in the calling code there is no object testing you send the same message to each object and let most of them ignore it. Two downsides that I can think of. First it can make the base class very cluttered with methods that have nothing to do with most of the hierarchy. Second it assumes all of the work can be done in the called method and doesn't handle the case where there might be additional context specific actions in the calling code (i.e. you want to do something in the UI and not the model). Have methods on the class to uniquely identify the objects. This could include methods like ClassName() which return a string with the class name or other return values like enums or booleans (IsImage()). The benefit is that the calling code can use if or switch statements to filter objects to perform class specific actions. The downside is that for every new class you need to implement these methods and can look cluttered. Also performance could be less than some of the other options. Use language features to identify objects. This includes reflection and language operators to identify the objects. For example in C# there is the is operator that returns true if the instance matches the specified class. The benefit is no additional code to implement in your object hierarchy. The only downside seems to be the lack of using something like a switch statement and the fact that your calling code is a little more cluttered. Are there other strategies I am missing? Thoughts on best approaches?

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• What is the motivation behind "Use Extension Methods Sparingly?"

  - by Robert Harvey

  I find them a very natural way to extend existing classes, especially when you just need to "spot-weld" some functionality onto an existing class. Microsoft says, "In general, we recommend that you implement extension methods sparingly and only when you have to." And yet extension methods form the foundation of Linq; in fact, Linq was the reason extension methods were created. Are there specific design criteria where using extension methods are perferred over inheritance or composition? Under what criteria are they discouraged?

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• Various Methods of Building a Website - Things to Consider Before Getting Started

  Building a website doesn't have to be difficult. There are many different types of websites and various methods of making them. A site can be a simple blog, personal web page, online store, a professional, business website, and so forth. Read on to learn about all the different ways you can make a site. Even if you're completely new to web development, you can try some of these methods.

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• LINQ – TakeWhile and SkipWhile methods

  - by nmarun

  I happened to read about these methods on Vikram's blog and tried testing it. Somehow when I saw the output, things did not seem to add up right. I’m writing this blog to show the actual workings of these methods. Let’s take the same example as showing in Vikram’s blog and I’ll build around it. 1: int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 2:  3: foreach(var number in numbers.TakeWhile(n => n < 7)) 4: { 5: Console.WriteLine(number); 6: } Now, the way I (incorrectly) read the upper bound condition in the foreach loop was: ‘Give me all numbers that pass the condition of n<7’. So I was expecting the answer to be: 5, 4, 1, 3, 2, 0. But when I run the application, I see only: 5, 4, 1,3. Turns out I was wrong (happens at least once a day). The documentation on the method says ‘Returns elements from a sequence as long as a specified condition is true. To show in code, my interpretation was the below code’: 1: foreach (var number in numbers) 2: { 3: if (number < 7) 4: { 5: Console.WriteLine(number); 6: } 7: } But the actual implementation is: 1: foreach(var number in numbers) 2: { 3: if(number < 7) 4: { 5: Console.WriteLine(number); 6: break; 7: } 8: } So there it is, another situation where one simple word makes a difference of a whole world. The SkipWhile method has been implemented in a similar way – ‘Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements’ and not ‘Bypasses elements in a sequence where a specified condition is true and then returns the remaining elements’. (Subtle.. very very subtle). It’s feels strange saying this, but hope very few require to read this article to understand these methods.

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• Deprecated Methods in Code Base

  - by Jamie Taylor

  A lot of the code I've been working on recently, both professionally (read: at work) and in other spheres (read: at home, for friends/family/etc, or NOT FOR WORK), has been worked on, redesigned and re-implemented several times - where possible/required. This has been in an effort to make things smaller, faster more efficient, better and closer to spec (when requirements have changed). A down side to this is that I now have several code bases that have deprecated method blocks (and in some places small objects). I'm looking at making this code maintainable and easy to roll back on changes. I'm already using version control software in both instances, but I'm left wondering if there are any specific techniques that have been used by others for keeping the superseded methods without increasing the size of compiled outputs? At the minute, I'm simply wrapping the old code in C style multi line comments. Here's an example of what I mean (C style, psuedo-code): void main () { //Do some work //Foo(); //Deprecated method call Bar(); //New method } /***** Deprecated code ***** /// Summary of Method void Foo() { //Do some work } ***** Deprecated Code *****/ /// Summary of method void Bar() { //Do some work } I've added a C style example, simply because I'm more confident with the C style languages. I'm trying to put this question across as language agnostic (hence the tag), and would prefer language agnostic answers, if possible - since I see this question as more of a techniques and design question. I'd like to keep the old methods and blocks for a bunch of reasons, chief amongst them being the ability to quickly restore an older working method in the case of some tests failing, or some unforeseen circumstance. Is there a better way to do this (that multi line comments)? Are there any tools that will allow me to store these old methods in separate files? Is that even a good idea?

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• Extension Methods in Dot Net 2.0

  - by Tom Hines

  Not that anyone would still need this, but in case you have a situation where the code MUST be .NET 2.0 compliant and you want to use a cool feature like Extension methods, there is a way.  I saw this article when looking for ways to create extension methods in C++, C# and VB:  http://msdn.microsoft.com/en-us/magazine/cc163317.aspx The author shows a simple  way to declare/define the ExtensionAttribute so it's available to 2.0 .NET code. Please read the article to learn about the when and why and use the content below to learn HOW. In the next post, I'll demonstrate cross-language calling of extension methods. Here is a version of it in C# First, here's the project showing there's no VOODOO included: using System; namespace System.Runtime.CompilerServices {    [       AttributeUsage(          AttributeTargets.Assembly          | AttributeTargets.Class          | AttributeTargets.Method,       AllowMultiple = false, Inherited = false)    ]    class ExtensionAttribute : Attribute{} } namespace TestTwoDotExtensions {    public static class Program    {       public static void DoThingCS(this string str)       {          Console.WriteLine("2.0\t{0:G}\t2.0", str);       }       static void Main(string[] args)       {          "asdf".DoThingCS();       }    } }   Here is the C++ version: // TestTwoDotExtensions_CPP.h #pragma once using namespace System; namespace System {        namespace Runtime {               namespace CompilerServices {               [                      AttributeUsage(                            AttributeTargets::Assembly                             | AttributeTargets::Class                            | AttributeTargets::Method,                      AllowMultiple = false, Inherited = false)               ]               public ref class ExtensionAttribute : Attribute{};               }        } } using namespace System::Runtime::CompilerServices; namespace TestTwoDotExtensions_CPP { public ref class CTestTwoDotExtensions_CPP {    public:            [ExtensionAttribute] // or [Extension]            static void DoThingCPP(String^ str)    {       Console::WriteLine("2.0\t{0:G}\t2.0", str);    } }; }

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• C#/.NET Little Wonders: Tuples and Tuple Factory Methods

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can really help improve your code by making it easier to write and maintain.  This week, we look at the System.Tuple class and the handy factory methods for creating a Tuple by inferring the types. What is a Tuple? The System.Tuple is a class that tends to inspire a reaction in one of two ways: love or hate.  Simply put, a Tuple is a data structure that holds a specific number of items of a specific type in a specific order.  That is, a Tuple<int, string, int> is a tuple that contains exactly three items: an int, followed by a string, followed by an int.  The sequence is important not only to distinguish between two members of the tuple with the same type, but also for comparisons between tuples.  Some people tend to love tuples because they give you a quick way to combine multiple values into one result.  This can be handy for returning more than one value from a method (without using out or ref parameters), or for creating a compound key to a Dictionary, or any other purpose you can think of.  They can be especially handy when passing a series of items into a call that only takes one object parameter, such as passing an argument to a thread's startup routine.  In these cases, you do not need to define a class, simply create a tuple containing the types you wish to return, and you are ready to go? On the other hand, there are some people who see tuples as a crutch in object-oriented design.  They may view the tuple as a very watered down class with very little inherent semantic meaning.  As an example, what if you saw this in a piece of code: 1: var x = new Tuple<int, int>(2, 5); What are the contents of this tuple?  If the tuple isn't named appropriately, and if the contents of each member are not self evident from the type this can be a confusing question.  The people who tend to be against tuples would rather you explicitly code a class to contain the values, such as: 1: public sealed class RetrySettings 2: { 3: public int TimeoutSeconds { get; set; } 4: public int MaxRetries { get; set; } 5: } Here, the meaning of each int in the class is much more clear, but it's a bit more work to create the class and can clutter a solution with extra classes. So, what's the correct way to go?  That's a tough call.  You will have people who will argue quite well for one or the other.  For me, I consider the Tuple to be a tool to make it easy to collect values together easily.  There are times when I just need to combine items for a key or a result, in which case the tuple is short lived and so the meaning isn't easily lost and I feel this is a good compromise.  If the scope of the collection of items, though, is more application-wide I tend to favor creating a full class. Finally, it should be noted that tuples are immutable.  That means they are assigned a value at construction, and that value cannot be changed.  Now, of course if the tuple contains an item of a reference type, this means that the reference is immutable and not the item referred to. Tuples from 1 to N Tuples come in all sizes, you can have as few as one element in your tuple, or as many as you like.  However, since C# generics can't have an infinite generic type parameter list, any items after 7 have to be collapsed into another tuple, as we'll show shortly. So when you declare your tuple from sizes 1 (a 1-tuple or singleton) to 7 (a 7-tuple or septuple), simply include the appropriate number of type arguments: 1: // a singleton tuple of integer 2: Tuple<int> x; 3:  4: // or more 5: Tuple<int, double> y; 6:  7: // up to seven 8: Tuple<int, double, char, double, int, string, uint> z; Anything eight and above, and we have to nest tuples inside of tuples.  The last element of the 8-tuple is the generic type parameter Rest, this is special in that the Tuple checks to make sure at runtime that the type is a Tuple.  This means that a simple 8-tuple must nest a singleton tuple (one of the good uses for a singleton tuple, by the way) for the Rest property. 1: // an 8-tuple 2: Tuple<int, int, int, int, int, double, char, Tuple<string>> t8; 3:  4: // an 9-tuple 5: Tuple<int, int, int, int, double, int, char, Tuple<string, DateTime>> t9; 6:  7: // a 16-tuple 8: Tuple<int, int, int, int, int, int, int, Tuple<int, int, int, int, int, int, int, Tuple<int,int>>> t14; Notice that on the 14-tuple we had to have a nested tuple in the nested tuple.  Since the tuple can only support up to seven items, and then a rest element, that means that if the nested tuple needs more than seven items you must nest in it as well.  Constructing tuples Constructing tuples is just as straightforward as declaring them.  That said, you have two distinct ways to do it.  The first is to construct the tuple explicitly yourself: 1: var t3 = new Tuple<int, string, double>(1, "Hello", 3.1415927); This creates a triple that has an int, string, and double and assigns the values 1, "Hello", and 3.1415927 respectively.  Make sure the order of the arguments supplied matches the order of the types!  Also notice that we can't half-assign a tuple or create a default tuple.  Tuples are immutable (you can't change the values once constructed), so thus you must provide all values at construction time. Another way to easily create tuples is to do it implicitly using the System.Tuple static class's Create() factory methods.  These methods (much like C++'s std::make_pair method) will infer the types from the method call so you don't have to type them in.  This can dramatically reduce the amount of typing required especially for complex tuples! 1: // this 4-tuple is typed Tuple<int, double, string, char> 2: var t4 = Tuple.Create(42, 3.1415927, "Love", 'X'); Notice how much easier it is to use the factory methods and infer the types?  This can cut down on typing quite a bit when constructing tuples.  The Create() factory method can construct from a 1-tuple (singleton) to an 8-tuple (octuple), which of course will be a octuple where the last item is a singleton as we described before in nested tuples. Accessing tuple members Accessing a tuple's members is simplicity itself… mostly.  The properties for accessing up to the first seven items are Item1, Item2, …, Item7.  If you have an octuple or beyond, the final property is Rest which will give you the nested tuple which you can then access in a similar matter.  Once again, keep in mind that these are read-only properties and cannot be changed. 1: // for septuples and below, use the Item properties 2: var t1 = Tuple.Create(42, 3.14); 3:  4: Console.WriteLine("First item is {0} and second is {1}", 5: t1.Item1, t1.Item2); 6:  7: // for octuples and above, use Rest to retrieve nested tuple 8: var t9 = new Tuple<int, int, int, int, int, int, int, 9: Tuple<int, int>>(1,2,3,4,5,6,7,Tuple.Create(8,9)); 10:  11: Console.WriteLine("The 8th item is {0}", t9.Rest.Item1); Tuples are IStructuralComparable and IStructuralEquatable Most of you know about IComparable and IEquatable, what you may not know is that there are two sister interfaces to these that were added in .NET 4.0 to help support tuples.  These IStructuralComparable and IStructuralEquatable make it easy to compare two tuples for equality and ordering.  This is invaluable for sorting, and makes it easy to use tuples as a compound-key to a dictionary (one of my favorite uses)! Why is this so important?  Remember when we said that some folks think tuples are too generic and you should define a custom class?  This is all well and good, but if you want to design a custom class that can automatically order itself based on its members and build a hash code for itself based on its members, it is no longer a trivial task!  Thankfully the tuple does this all for you through the explicit implementations of these interfaces. For equality, two tuples are equal if all elements are equal between the two tuples, that is if t1.Item1 == t2.Item1 and t1.Item2 == t2.Item2, and so on.  For ordering, it's a little more complex in that it compares the two tuples one at a time starting at Item1, and sees which one has a smaller Item1.  If one has a smaller Item1, it is the smaller tuple.  However if both Item1 are the same, it compares Item2 and so on. For example: 1: var t1 = Tuple.Create(1, 3.14, "Hi"); 2: var t2 = Tuple.Create(1, 3.14, "Hi"); 3: var t3 = Tuple.Create(2, 2.72, "Bye"); 4:  5: // true, t1 == t2 because all items are == 6: Console.WriteLine("t1 == t2 : " + t1.Equals(t2)); 7:  8: // false, t1 != t2 because at least one item different 9: Console.WriteLine("t2 == t2 : " + t2.Equals(t3)); The actual implementation of IComparable, IEquatable, IStructuralComparable, and IStructuralEquatable is explicit, so if you want to invoke the methods defined there you'll have to manually cast to the appropriate interface: 1: // true because t1.Item1 < t3.Item1, if had been same would check Item2 and so on 2: Console.WriteLine("t1 < t3 : " + (((IComparable)t1).CompareTo(t3) < 0)); So, as I mentioned, the fact that tuples are automatically equatable and comparable (provided the types you use define equality and comparability as needed) means that we can use tuples for compound keys in hashing and ordering containers like Dictionary and SortedList: 1: var tupleDict = new Dictionary<Tuple<int, double, string>, string>(); 2:  3: tupleDict.Add(t1, "First tuple"); 4: tupleDict.Add(t2, "Second tuple"); 5: tupleDict.Add(t3, "Third tuple"); Because IEquatable defines GetHashCode(), and Tuple's IStructuralEquatable implementation creates this hash code by combining the hash codes of the members, this makes using the tuple as a complex key quite easy!  For example, let's say you are creating account charts for a financial application, and you want to cache those charts in a Dictionary based on the account number and the number of days of chart data (for example, a 1 day chart, 1 week chart, etc): 1: // the account number (string) and number of days (int) are key to get cached chart 2: var chartCache = new Dictionary<Tuple<string, int>, IChart>(); Summary The System.Tuple, like any tool, is best used where it will achieve a greater benefit.  I wouldn't advise overusing them, on objects with a large scope or it can become difficult to maintain.  However, when used properly in a well defined scope they can make your code cleaner and easier to maintain by removing the need for extraneous POCOs and custom property hashing and ordering. They are especially useful in defining compound keys to IDictionary implementations and for returning multiple values from methods, or passing multiple values to a single object parameter. Tweet Technorati Tags: C#,.NET,Tuple,Little Wonders

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• Functional Methods on Collections

  - by GlenPeterson

  I'm learning Scala and am a little bewildered by all the methods (higher-order functions) available on the collections. Which ones produce more results than the original collection, which ones produce less, and which are most appropriate for a given problem? Though I'm studying Scala, I think this would pertain to most modern functional languages (Clojure, Haskell) and also to Java 8 which introduces these methods on Java collections. Specifically, right now I'm wondering about map with filter vs. fold/reduce. I was delighted that using foldRight() can yield the same result as a map(...).filter(...) with only one traversal of the underlying collection. But a friend pointed out that foldRight() may force sequential processing while map() is friendlier to being processed by multiple processors in parallel. Maybe this is why mapReduce() is so popular? More generally, I'm still sometimes surprised when I chain several of these methods together to get back a List(List()) or to pass a List(List()) and get back just a List(). For instance, when would I use: collection.map(a => a.map(b => ...)) vs. collection.map(a => ...).map(b => ...) The for/yield command does nothing to help this confusion. Am I asking about the difference between a "fold" and "unfold" operation? Am I trying to jam too many questions into one? I think there may be an underlying concept that, if I understood it, might answer all these questions, or at least tie the answers together.

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• Why you shouldn't add methods to interfaces in APIs

  - by Simon Cooper

  It is an oft-repeated maxim that you shouldn't add methods to a publically-released interface in an API. Recently, I was hit hard when this wasn't followed. As part of the work on ApplicationMetrics, I've been implementing auto-reporting of MVC action methods; whenever an action was called on a controller, ApplicationMetrics would automatically report it without the developer needing to add manual ReportEvent calls. Fortunately, MVC provides easy hook when a controller is created, letting me log when it happens - the IControllerFactory interface. Now, the dll we provide to instrument an MVC webapp has to be compiled against .NET 3.5 and MVC 1, as the lowest common denominator. This MVC 1 dll will still work when used in an MVC 2, 3 or 4 webapp because all MVC 2+ webapps have a binding redirect redirecting all references to previous versions of System.Web.Mvc to the correct version, and type forwards taking care of any moved types in the new assemblies. Or at least, it should. IControllerFactory In MVC 1 and 2, IControllerFactory was defined as follows: public interface IControllerFactory { IController CreateController(RequestContext requestContext, string controllerName); void ReleaseController(IController controller); } So, to implement the logging controller factory, we simply wrap the existing controller factory: internal sealed class LoggingControllerFactory : IControllerFactory { private readonly IControllerFactory m_CurrentController; public LoggingControllerFactory(IControllerFactory currentController) { m_CurrentController = currentController; } public IController CreateController( RequestContext requestContext, string controllerName) { // log the controller being used FeatureSessionData.ReportEvent("Controller used:", controllerName); return m_CurrentController.CreateController(requestContext, controllerName); } public void ReleaseController(IController controller) { m_CurrentController.ReleaseController(controller); } } Easy. This works as expected in MVC 1 and 2. However, in MVC 3 this type was throwing a TypeLoadException, saying a method wasn't implemented. It turns out that, in MVC 3, the definition of IControllerFactory was changed to this: public interface IControllerFactory { IController CreateController(RequestContext requestContext, string controllerName); SessionStateBehavior GetControllerSessionBehavior( RequestContext requestContext, string controllerName); void ReleaseController(IController controller); } There's a new method in the interface. So when our MVC 1 dll was redirected to reference System.Web.Mvc v3, LoggingControllerFactory tried to implement version 3 of IControllerFactory, was missing the GetControllerSessionBehaviour method, and so couldn't be loaded by the CLR. Implementing the new method Fortunately, there was a workaround. Because interface methods are normally implemented implicitly in the CLR, if we simply declare a virtual method matching the signature of the new method in MVC 3, then it will be ignored in MVC 1 and 2 and implement the extra method in MVC 3: internal sealed class LoggingControllerFactory : IControllerFactory { ... public virtual SessionStateBehaviour GetControllerSessionBehaviour( RequestContext requestContext, string controllerName) {} ... } However, this also has problems - the SessionStateBehaviour type only exists in .NET 4, and we're limited to .NET 3.5 by support for MVC 1 and 2. This means that the only solutions to support all MVC versions are: Construct the LoggingControllerFactory type at runtime using reflection Produce entirely separate dlls for MVC 1&2 and MVC 3. Ugh. And all because of that blasted extra method! Another solution? Fortunately, in this case, there is a third option - System.Web.Mvc also provides a DefaultControllerFactory type that can provide the implementation of GetControllerSessionBehaviour for us in MVC 3, while still allowing us to override CreateController and ReleaseController. However, this does mean that LoggingControllerFactory won't be able to wrap any calls to GetControllerSessionBehaviour. This is an acceptable bug, given the other options, as very few developers will be overriding GetControllerSessionBehaviour in their own custom controller factory. So, if you're providing an interface as part of an API, then please please please don't add methods to it. Especially if you don't provide a 'default' implementing type. Any code compiled against the previous version that can't be updated will have some very tough decisions to make to support both versions.

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• Why do some programmers think there is a contrast between theory and practice?

  - by Giorgio

  Comparing software engineering with civil engineering, I was surprised to observe a different way of thinking: any civil engineer knows that if you want to build a small hut in the garden you can just get the materials and go build it whereas if you want to build a 10-storey house you need to do quite some maths to be sure that it won't fall apart. In contrast, speaking with some programmers or reading blogs or forums I often find a wide-spread opinion that can be formulated more or less as follows: theory and formal methods are for mathematicians / scientists while programming is more about getting things done. What is normally implied here is that programming is something very practical and that even though formal methods, mathematics, algorithm theory, clean / coherent programming languages, etc, may be interesting topics, they are often not needed if all one wants is to get things done. According to my experience, I would say that while you do not need much theory to put together a 100-line script (the hut), in order to develop a complex application (the 10-storey building) you need a structured design, well-defined methods, a good programming language, good text books where you can look up algorithms, etc. So IMO (the right amount of) theory is one of the tools for getting things done. So my question is why do some programmers think that there is a contrast between theory (formal methods) and practice (getting things done)? Is software engineering (building software) perceived by many as easy compared to, say, civil engineering (building houses)? Or are these two disciplines really different (apart from mission-critical software, software failure is much more acceptable than building failure)?

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• Should I use formal methods on my software project?

  - by Michael

  Our client wants us to build a web-based, rich internet application for gathering software requirements. Basically it's a web-based case tool that follows a specific process for getting requirements from stakeholders. I'm the project manager and we're still in the early phases of the project. I've been thinking about using formal methods to help clarify the requirements for the tool for both my client and the developers. By formal methods I mean some form of modeling, possibly something mathematically-based. Some of the things I've read about and are considering include Z (http://en.wikipedia.org/wiki/Z_notation), state machines, UML 2.0 (possibly with extensions such as OCL), Petri nets, and some coding-level stuff like contracts and pre and post conditions. Is there anything else I should consider? The developers are experienced but depending on the formalism used they may have to learn some math. I'm trying to determine whether it's worth while for me to use formal methods on this project and if so, to what extent. I know "it depends" so the most helpful answers for me is a yes/no and supporting arguments. Would you use formal methods if you were on this project?

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• Can static methods be called using object/instance in .NET

  Ans is Yes and No   Yes in C++, Java and VB.NET No in C#   This is only compiler restriction in c#. You might see in some websites that we can break this restriction using reflection and delegates, but we can’t, according to my little research J I shall try to explain you…   Following is code sample to break this rule using reflection, it seems that it is possible to call a static method using an object, p1 using System; namespace T {     class Program     {         static void Main()         {             var p1 = new Person() { Name = "Smith" };             typeof(Person).GetMethod("TestStatMethod").Invoke(p1, new object[] { });                     }         class Person         {             public string Name { get; set; }             public static void TestStatMethod()             {                 Console.WriteLine("Hello");             }         }     } } but I do not think so this method is being called using p1 rather Type Name “Person”. I shall try to prove this… look at another example…  Test2 has been inherited from Test1. Let’s see various scenarios… Scenario1 using System; namespace T {     class Program     {         static void Main()         {             Test1 t = new Test1();            typeof(Test2).GetMethod("Method1").Invoke(t,                                  new object[] { });         }     }     class Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method1");         }     }       class Test2 : Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method2");         }     } } Output:   At test1::Method2 Scenario2         static void Main()         {             Test2 t = new Test2();            typeof(Test2).GetMethod("Method1").Invoke(t,                                          new object[] { });         }   Output:   At test1::Method2   Scenario3         static void Main()         {             Test1 t = new Test2();            typeof(Test2).GetMethod("Method1").Invoke(t,                             new object[] { });         }   Output: At test1::Method2 In all above scenarios output is same, that means, Reflection also not considering the object what you pass to Invoke method in case of static methods. It is always considering the type which you specify in typeof(). So, what is the use passing instance to “Invoke”. Let see below sample using System; namespace T {     class Program     {         static void Main()         {            typeof(Test2).GetMethod("Method1").                Invoke(null, new object[] { });         }     }       class Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method1");         }     }     class Test2 : Test1     {         public static void Method1()         {             Console.WriteLine("At test1::Method2");         }     } }   Output is   At test1::Method2   I was able to call Invoke “Method1” of Test2 without any object.  Yes, there no wonder here as Method1 is static. So we may conclude that static methods cannot be called using instances (only in c#) Why Microsoft has restricted it in C#? Ans: Really there Is no use calling static methods using objects because static methods are stateless. but still Java and C++ latest compilers allow calling static methods using instances. Java sample class Test {      public static void main(String str[])      {            Person p = new Person();            System.out.println(p.GetCount());      } }   class Person {   public static int GetCount()   {      return 100;   } }   Output          100 span.fullpost {display:none;}

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• System.Reflection - Global methods aren't available for reflection

  - by mrjoltcola

  I have an issue with a semantic gap between the CLR and System.Reflection. System.Reflection does not (AFAIK) support reflecting on global methods in an assembly. At the assembly level, I must start with the root types. My compiler can produce assemblies with global methods, and my standard bootstrap lib is a dll that includes some global methods. My compiler uses System.Reflection to import assembly metadata at compile time. It seems if I depend on System.Reflection, global methods are not a possibility. The cleanest solution is to convert all of my standard methods to class static methods, but the point is, my language allows global methods, and the CLR supports it, but System.Reflection leaves a gap. ildasm shows the global methods just fine, but I assume it does not use System.Reflection itself and goes right to the metadata and bytecode. Besides System.Reflection, is anyone aware of any other 3rd party reflection or disassembly libs that I could make use of (assuming I will eventually release my compiler as free, BSD licensed open source).

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