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• Appropriate uses of Monad `fail` vs. MonadPlus `mzero`

  - by jberryman

  This is a question that has come up several times for me in the design code, especially libraries. There seems to be some interest in it so I thought it might make a good community wiki. The fail method in Monad is considered by some to be a wart; a somewhat arbitrary addition to the class that does not come from the original category theory. But of course in the current state of things, many Monad types have logical and useful fail instances. The MonadPlus class is a sub-class of Monad that provides an mzero method which logically encapsulates the idea of failure in a monad. So a library designer who wants to write some monadic code that does some sort of failure handling can choose to make his code use the fail method in Monad or restrict his code to the MonadPlus class, just so that he can feel good about using mzero, even though he doesn't care about the monoidal combining mplus operation at all. Some discussions on this subject are in this wiki page about proposals to reform the MonadPlus class. So I guess I have one specific question: What monad instances, if any, have a natural fail method, but cannot be instances of MonadPlus because they have no logical implementation for mplus? But I'm mostly interested in a discussion about this subject. Thanks! EDIT: One final thought occured to me. I recently learned (even though it's right there in the docs for fail) that monadic "do" notation is desugared in such a way that pattern match failures, as in (x:xs) <- return [] call the monad's fail. It seems like the language designers must have been strongly influenced by the prospect of some automatic failure handling built in to haskell's syntax in their inclusion of fail in Monad.

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• How to work with CTE. There is some error related to anchor.

  - by Shantanu Gupta

  I am creating a hierarchy representaion of a column. But an error occurs Details are Msg 240, Level 16, State 1, Line 1 Types don't match between the anchor and the recursive part in column "DISPLAY" of recursive query "CTE". I know there is some typecasting error. But I dont know how to remove error. Please just dont only sort out my error. I need explanation why this error is coming. When this error occurs. I am trying to sort table on the basis of sort col that i m introducing. I want to add '-' at every level and want to sort accordingly. Please help WITH CTE (PK_CATEGORY_ID, [DESCRIPTION], FK_CATEGORY_ID, DISPLAY, SORT, DEPTH) AS ( SELECT PK_CATEGORY_ID, [DESCRIPTION], FK_CATEGORY_ID, '-' AS DISPLAY, '--' AS SORT, 0 AS DEPTH FROM dbo.L_CATEGORY_TYPE WHERE FK_CATEGORY_ID IS NULL UNION ALL SELECT T.PK_CATEGORY_ID, T.[DESCRIPTION], T.FK_CATEGORY_ID, CAST(DISPLAY+T.[DESCRIPTION] AS VARCHAR(1000)), '--' AS SORT, C.DEPTH +1 FROM dbo.L_CATEGORY_TYPE T JOIN CTE C ON C.PK_CATEGORY_ID = T.FK_CATEGORY_ID --SELECT T.PK_CATEGORY_ID, C.SORT+T.[DESCRIPTION], T.FK_CATEGORY_ID --, CAST('--' + C.SORT AS VARCHAR(1000)) AS SORT, CAST(DEPTH +1 AS INT) AS DEPTH --FROM dbo.L_CATEGORY_TYPE T JOIN CTE C ON C.FK_CATEGORY_ID = T.PK_CATEGORY_ID ) SELECT PK_CATEGORY_ID, [DESCRIPTION], FK_CATEGORY_ID, DISPLAY, SORT, DEPTH FROM CTE ORDER BY SORT

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• Using Generics to return a literal string or from Dictionary<string, object>

  - by Mike

  I think I outsmarted myself this time. Feel free to edit the title also I could not think of a good one. I am reading from a file and then in that file will be a string because its like an xml file. But in the file will be a literal value or a "command" to get the value from the workContainer so <Email>[email protected]</Email> or <Email>[? MyEmail ?]</Email> What I wanted to do instead of writing ifs all over the place to put it in a generic function so logic is If Container command grab from container else grab string and convert to desired type Its up to the user to ensure the file is ok and the type is correct so another example is so <Answer>3</Answer> or <Answer>[? NumberOfSales ?]</Answer> This is the procedure I started to work on public class WorkContainer:Dictionary<string, object> { public T GetKeyValue<T>(string Parameter) { if (Parameter.StartsWith("[? ")) { string key = Parameter.Replace("[? ", "").Replace(" ?]", ""); if (this.ContainsKey(key)) { return (T)this[key]; } else { // may throw error for value types return default(T); } } else { // Does not Compile if (typeof(T) is string) { return Parameter } // OR return (T)Parameter } } } The Call would be mail.To = container.GetKeyValue<string>("[email protected]"); or mail.To = container.GetKeyValue<string>("[? MyEmail ?]"); int answer = container.GetKeyValue<int>("3"); or answer = container.GetKeyValue<int>("[? NumberOfSales ?]"); But it does not compile?

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• C++ Templates: Convincing self against code bloat

  - by ArunSaha

  I have heard about code bloats in context of C++ templates. I know that is not the case with modern C++ compilers. But, I want to construct an example and convince myself. Lets say we have a class template< typename T, size_t N > class Array { public: T * data(); private: T elems_[ N }; }; template< typename T, size_t N > T * Array<T>::data() { return elems_; } Further, let's say types.h contains typedef Array< int, 100 > MyArray; x.cpp contains MyArray ArrayX; and y.cpp contains MyArray ArrayY; Now, how can I verify that the code space for MyArray::data() is same for both ArrayX and ArrayY? What else I should know and verify from this (or other similar simple) examples? If there is any g++ specific tips, I am interested for that too. PS: Regarding bloat, I am concerned even for the slightest of bloats, since I come from embedded context.

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• which one of these is an example of coercion

  - by user1890210

  I have been pondering a multiple choice question on coercion. One of the 4 examples a,b,c or d is an example of coercion. I narrowed it down to A or B. But I am having a problem choosing between the two. Cane someone please explain why one is coercion and one isn't. A) string s="tomat"; char c='o'; s=s+c; I thought A could be correct because we have two different types, character and string, being added. Meaning that c is promoted to string, hence coercion. B) double x=1.0; double y=2.0; int i=(int)(x+y); I also thought B was the correct answer because the double (x+y) is being turned into a int to be placed in i. But I thought this could be wrong because its being done actively through use of (int) rather than passively such as "int i = x + y" I'll list the other two options, even though I believe that neither one is the correct answer C) char A=0x20; A = A << 1 | 0x01; cout << A << endl; D) double x=1.0; double y=x+1; return 0; I'm not just looking for an answer, but an explanation. I have read tons of things on coercion and A and B both look like the right answer. So why is one correct and the other not.

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• Can a T-SQL variable represent an entire row?

  - by elbillaf

  I'm coding for MS SQL Server 10. I have two databases that contain dozens of tables. Each table in one database contains a table with the same name in the other database. Tables with the same name have identical format (fields and data types). The contents of the two tables are similar but not identical. I need to update one based on changes made to the other, but only under certain circumstances. I think I want to use a cursor for this, but I can't find a good example to go by. So far, the MSDN examples are reading one field at a time into a variable. I do need to be able to read /modify two fields which are identical in each table, but I gotta believe there's something less tedious than declaring variables for every field of every table. I would like to be able to FETCH an entire row, check a couple of fields and then make a decision of whether I want to write the entire row to the other table after changing two fields - but do I have to declare variables for EVERY field I want to fetch / write? There's no way to just FETCH an entire row and write an entire row?

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• Javascript cloned object looses its prototype functions

  - by Jake M

  I am attempting to clone an object in Javascript. I have made my own 'class' that has prototype functions. My Problem: When I clone an object, the clone cant access/call any prototype functions. I get an error when I go to access a prototype function of the clone: clone.render is not a function Can you tell me how I can clone an object and keep its prototype functions This simple JSFiddle demonstrates the error I get: http://jsfiddle.net/VHEFb/1/ function cloneObject(obj) { // Handle the 3 simple types, and null or undefined if (null == obj || "object" != typeof obj) return obj; // Handle Date if (obj instanceof Date) { var copy = new Date(); copy.setTime(obj.getTime()); return copy; } // Handle Array if (obj instanceof Array) { var copy = []; for (var i = 0, len = obj.length; i < len; ++i) { copy[i] = cloneObject(obj[i]); } return copy; } // Handle Object if (obj instanceof Object) { var copy = {}; for (var attr in obj) { if (obj.hasOwnProperty(attr)) copy[attr] = cloneObject(obj[attr]); } return copy; } throw new Error("Unable to copy obj! Its type isn't supported."); } function MyObject(name) { this.name = name; // I have arrays stored in this object also so a simple cloneNode(true) call wont copy those // thus the need for the function cloneObject(); } MyObject.prototype.render = function() { alert("Render executing: "+this.name); } var base = new MyObject("base"); var clone = cloneObject(base); clone.name = "clone"; base.render(); clone.render(); // Error here: "clone.render is not a function"

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• How do you pass a generic delegate argument to a method in .NET 2.0

  - by Seth Spearman

  Hello, I have a class with a delegate declaration as follows... Public Class MyClass Public Delegate Function Getter(Of TResult)() As TResult 'the following code works. Public Shared Sub MyMethod(ByVal g As Getter(Of Boolean)) 'do stuff End Sub End Class However, I do not want to explicitly type the Getter delegate in the Method call. Why can I not declare the parameter as follows... ... (ByVal g As Getter(Of TResult)) Is there a way to do it? My end goal was to be able to set a delegate for property setters and getters in the called class. But my reading indicates you can't do that. So I put setter and getter methods in that class and then I want the calling class to set the delegate argument and then invoke. Is there a best practice for doing this. I realize in the above example that I can set set the delegate variable from the calling class...but I am trying to create a singleton with tight encapsulation. For the record, I can't use any of the new delegate types declared in .net35. Answers in C# are welcome. Any thoughts? Seth

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• Basic problems (type inference or something else?) in Objective-C/Cocoa.

  - by Matt

  Hi, Apologies for how basic these questions are to some. Just started learning Cocoa, working through Hillegass' book, and am trying to write my first program (a GUI Cocoa app that counts the number of characters in a string). I tried this: NSString *string = [textField stringValue]; NSUInteger *stringLength = [string length]; NSString *countString = (@"There are %u characters",stringLength); [label setStringValue:countString]; But I'm getting errors like: Incompatible pointer conversion initializing 'NSUInteger' (aka 'unsigned long'), expected 'NSUInteger *'[-pedantic] for the first line, and this for the second line: Incompatible pointer types initializing 'NSUInteger *', expected 'NSString *' [-pedantic] I did try this first, but it didn't work either: [label setStringValue:[NSString stringWithFormat:@"There are %u characters",[[textField stringValue] length]]] On a similar note, I've only written in easy scripting languages before now, and I'm not sure when I should be allocing/initing objects and when I shouldn't. For example, when is it okay to do this: NSString *myString = @"foo"; or int *length = 5; instead of this: NSString *myString = [[NSString alloc] initWithString:"foo"]; And which ones should I be putting into the header files? I did check Apple's documentation, and CocoaDev, and the book I'm working for but without luck. Maybe I'm looking in the wrong places.. Thanks to anyone who takes the time to reply this: it's appreciated, and thanks for being patient with a beginner. We all start somewhere. EDIT Okay, I tried the following again: [label setStringValue:[NSString stringWithFormat:@"There are %u characters",[[textField stringValue] length]]] And it actually worked this time. Not sure why it didn't the first time, though I think I might have typed %d instead of %u by mistake. However I still don't understand why the code I posted at the top of my original post doesn't work, and I have no idea what the errors mean, and I'd very much like to know because it seems like I'm missing something important there.

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• Set service dependencies after install

  - by Dennis

  I have an application that runs as a Windows service. It stores various things settings in a database that are looked up when the service starts. I built the service to support various types of databases (SQL Server, Oracle, MySQL, etc). Often times end users choose to configure the software to use SQL Server (they can simply modify a config file with the connection string and restart the service). The problem is that when their machine boots up, often times SQL Server is started after my service so my service errors out on start up because it can't connect to the database. I know that I can specify dependencies for my service to help guide the Windows service manager to start the appropriate services before mine. However, I don't know what services to depend upon at install time (when my service is registered) since the user can change databases later on. So my question is: is there a way for the user to manually indicate the service dependencies based on the database that they are using? If not, what is the proper design approach that I should be taking? I've thought about trying to do something like wait 30 seconds after my service starts up before connecting to the database but this seems really flaky for various reasons. I've also considered trying to "lazily" connect to the database; the problem is that I need a connection immediately upon start up since the database contains various pieces of vital info that my service needs when it first starts. Any ideas?

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• What, if any, printable character did a user type based on the values in a given System.Windows.Form

  - by Corey Trager

  As a workaround for a problem, I think I have to handle KeyDown events to get the printable character the user actually typed. KeyDown supplies me with a KeyEventArgs object with the properities KeyCode, KeyData, KeyValue, Modifiers, Alt, Shift, Control. My first attempt was just to consider the KeyCode to be the ascii code, but KeyCode on my keyboard is 46, a period ("."), so I end up printing a period when the user types the delete key. So, I know my logic is inadequate. (For those who are curious, the problem is that I have my own combobox in a DataGridView's control collection and somehow SOME characters I type don't produce the KeyPress and TextChanged ComboBox events. These letters include Q, $, %.... This code will reproduce the problem. Generate a Form App and replace the ctor with this code. Run it, and try typing the letter Q into the two comboxes. public partial class Form1 : Form { ComboBox cmbInGrid; ComboBox cmbNotInGrid; DataGridView grid; public Form1() { InitializeComponent(); grid = new DataGridView(); cmbInGrid = new ComboBox(); cmbNotInGrid = new ComboBox(); cmbInGrid.Items.Add("a"); cmbInGrid.Items.Add("b"); cmbNotInGrid.Items.Add("c"); cmbNotInGrid.Items.Add("d"); this.Controls.Add(cmbNotInGrid); this.Controls.Add(grid); grid.Location = new Point(0, 100); this.grid.Controls.Add(cmbInGrid); }

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• Casting Type array to Generic array?

  - by George R

  The short version of the question - why can't I do this? I'm restricted to .NET 3.5. T[] genericArray; // Obviously T should be float! genericArray = new T[3]{ 1.0f, 2.0f, 0.0f }; // Can't do this either, why the hell not genericArray = new float[3]{ 1.0f, 2.0f, 0.0f }; Longer version - I'm working with the Unity engine here, although that's not important. What is - I'm trying to throw conversion between its fixed Vector2 (2 floats) and Vector3 (3 floats) and my generic Vector< class. I can't cast types directly to a generic array. using UnityEngine; public struct Vector { private readonly T[] _axes; #region Constructors public Vector(int axisCount) { this._axes = new T[axisCount]; } public Vector(T x, T y) { this._axes = new T[2] { x, y }; } public Vector(T x, T y, T z) { this._axes = new T[3]{x, y, z}; } public Vector(Vector2 vector2) { // This doesn't work this._axes = new T[2] { vector2.x, vector2.y }; } public Vector(Vector3 vector3) { // Nor does this this._axes = new T[3] { vector3.x, vector3.y, vector3.z }; } #endregion #region Properties public T this[int i] { get { return _axes[i]; } set { _axes[i] = value; } } public T X { get { return _axes[0];} set { _axes[0] = value; } } public T Y { get { return _axes[1]; } set { _axes[1] = value; } } public T Z { get { return this._axes.Length (Vector2 vector2) { Vector vector = new Vector(vector2); return vector; } public static explicit operator Vector(Vector3 vector3) { Vector vector = new Vector(vector3); return vector; } #endregion }

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• Java: Typecasting to Generics

  - by bguiz

  This method that uses method-level generics, that parses the values from a custom POJO, JXlistOfKeyValuePairs (which is exactly that). The only thing is that both the keys and values in JXlistOfKeyValuePairs are Strings. This method wants to taken in, in addition to the JXlistOfKeyValuePairs instance, a Class<T> that defines which data type to convert the values to (assume that only Boolean, Integer and Float are possible). It then outputs a HashMap with the specified type for the values in its entries. This is the code that I have got, and it is obviously broken. private <T extends Object> Map<String, T> fromListOfKeyValuePairs(JXlistOfKeyValuePairs jxval, Class<T> clasz) { Map<String, T> val = new HashMap<String, T>(); List<Entry> jxents = jxval.getEntry(); T value; String str; for (Entry jxent : jxents) { str = jxent.getValue(); value = null; if (clasz.isAssignableFrom(Boolean.class)) { value = (T)(Boolean.parseBoolean(str)); } else if (clasz.isAssignableFrom(Integer.class)) { value = (T)(Integer.parseInt(str)); } else if (clasz.isAssignableFrom(Float.class)) { value = (T)(Float.parseFloat(str)); } else { logger.warn("Unsupported value type encountered in key-value pairs, continuing anyway: " + clasz.getName()); } val.put(jxent.getKey(), value); } return val; } This is the bit that I want to solve: if (clasz.isAssignableFrom(Boolean.class)) { value = (T)(Boolean.parseBoolean(str)); } else if (clasz.isAssignableFrom(Integer.class)) { value = (T)(Integer.parseInt(str)); } I get: Inconvertible types required: T found: Boolean Also, if possible, I would like to be able to do this with more elegant code, avoiding Class#isAssignableFrom. Any suggestions? Sample method invocation: Map<String, Boolean> foo = fromListOfKeyValuePairs(bar, Boolean.class);

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• Using static variables for Strings

  - by Vivart

  below content is taken from Best practice: Writing efficient code but i didn't understand why private static String x = "example"; faster than private static final String x ="example"; Can anybody explain this. Using static variables for Strings When you define static fields (also called class fields) of type String, you can increase application speed by using static variables (not final) instead of constants (final). The opposite is true for primitive data types, such as int. For example, you might create a String object as follows: private static final String x = "example"; For this static constant (denoted by the final keyword), each time that you use the constant, a temporary String instance is created. The compiler eliminates "x" and replaces it with the string "example" in the bytecode, so that the BlackBerry® Java® Virtual Machine performs a hash table lookup each time that you reference "x". In contrast, for a static variable (no final keyword), the String is created once. The BlackBerry JVM performs the hash table lookup only when it initializes "x", so access is faster. private static String x = "example"; You can use public constants (that is, final fields), but you must mark variables as private.

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• OrderBy Linq.Expression as parameter = (Of Func(Of T,IComparable)) to perform LinqToEntity is not working

  - by NicoJuicy

  I'd like to get this working: Call: (Count & Page are used for pagination, so Count = 20 and Page = 1 for example, for the first 20 values). Sorting should be by name LeverancierService.GetLeveranciers(Function(el) el.Name, Count, Page) Equivalent in c#: LeverancierService.GetLeveranciers(el= el.Name, Count, Page) Method that gives an error (parameters shown above): Public Overridable Function GetAllPaged(orderby As Expression(Of Func(Of T, IComparable)), ByVal Count As Integer, ByVal Page As Integer) As IEnumerable(Of T) Return dbset.OrderBy(orderby).Skip((Page - 1) * Count).Take(Count).ToList() End Function Already tried changing it to this, but it gives the same error: Public Overridable Function GetAllPaged(Of TOrderBy)(orderby As Expression(Of Func(Of T, TOrderBy)), ByVal Count As Integer, ByVal Page As Integer) As IEnumerable(Of T) Return dbset.OrderBy(orderby).Skip((Page - 1) * Count).Take(Count).ToList() End Function Error: Unable to cast the type 'System.String' to type 'System.IComparable'. LINQ to Entities only supports casting Entity Data Model primitive types. Any idea how to do this? Extra info: I'm in a DDD-layered application, so the parameter should stay the same as the called method is an overridden interface (eg. if i change this, i have to do this for 200 times or so, because it's in VB.Net and not in C# (= 1 change) ) I know there is a way to change the expression to a string and then use DLinq (= Dynamic Linq), but that's not how it should be.

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• Checking if a file is a directory or just a file.

  - by Jookia

  I'm writing a program to check if something is a file or is a directory. Is there a better way to do it than this? #include <stdio.h> #include <sys/types.h> #include <dirent.h> #include <errno.h> int isFile(const char* name) { DIR* directory = opendir(name); if(directory != NULL) { closedir(directory); return 0; } if(errno == ENOTDIR) { return 1; } return -1; } int main(void) { const char* file = "./testFile"; const char* directory = "./"; printf("Is %s a file? %s.\n", file, ((isFile(file) == 1) ? "Yes" : "No")); printf("Is %s a directory? %s.\n", directory, ((isFile(directory) == 0) ? "Yes" : "No")); return 0; }

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• SSE (SIMD extensions) support in gcc

  - by goldenmean

  Hi, I see a code as below: include "stdio.h" #define VECTOR_SIZE 4 typedef float v4sf __attribute__ ((vector_size(sizeof(float)*VECTOR_SIZE))); // vector of four single floats typedef union f4vector { v4sf v; float f[VECTOR_SIZE]; } f4vector; void print_vector (f4vector *v) { printf("%f,%f,%f,%f\n", v->f[0], v->f[1], v->f[2], v->f[3]); } int main() { union f4vector a, b, c; a.v = (v4sf){1.2, 2.3, 3.4, 4.5}; b.v = (v4sf){5., 6., 7., 8.}; c.v = a.v + b.v; print_vector(&a); print_vector(&b); print_vector(&c); } This code builds fine and works expectedly using gcc (it's inbuild SSE / MMX extensions and vector data types. this code is doing a SIMD vector addition using 4 single floats. I want to understand in detail what does each keyword/function call on this typedef line means and does: typedef float v4sf __attribute__ ((vector_size(sizeof(float)*VECTOR_SIZE))); What is the vector_size() function return; What is the __attribute__ keyword for Here is the float data type being type defined to vfsf type? I understand the rest part. thanks, -AD

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• Fortran pointer as an argument to interface procedure

  - by icarusthecow

  Im trying to use interfaces to call different subroutines with different types, however, it doesnt seem to work when i use the pointer attribute. for example, take this sample code MODULE ptr_types TYPE, abstract :: parent INTEGER :: q END TYPE TYPE, extends(parent) :: child INTEGER :: m END TYPE INTERFACE ptr_interface MODULE PROCEDURE do_something END INTERFACE CONTAINS SUBROUTINE do_something(atype) CLASS(parent), POINTER :: atype ! code determines that this allocation is correct from input ALLOCATE(child::atype) WRITE (*,*) atype%q END SUBROUTINE END MODULE PROGRAM testpass USE ptr_types CLASS(child), POINTER :: ctype CALL ptr_interface(ctype) END PROGRAM This gives error Error: There is no specific subroutine for the generic 'ptr_interface' at (1) however if i remove the pointer attribute in the subroutine it compiles fine. Now, normally this wouldnt be a problem, but for my use case i need to be able to treat that argument as a pointer, mainly so i can allocate it if necessary. Any suggestions? Mind you I'm new to fortran so I may have missed something edit: forgot to put the allocation in the parents subroutine, the initial input is unallocated EDIT 2 this is my second attempt, with caller side casting MODULE ptr_types TYPE, abstract :: parent INTEGER :: q END TYPE TYPE, extends(parent) :: child INTEGER :: m END TYPE TYPE, extends(parent) :: second INTEGER :: meow END TYPE CONTAINS SUBROUTINE do_something(this, type_num) CLASS(parent), POINTER :: this INTEGER type_num IF (type_num == 0) THEN ALLOCATE (child::this) ELSE IF (type_num == 1) THEN ALLOCATE (second::this) ENDIF END SUBROUTINE END MODULE PROGRAM testpass USE ptr_types CLASS(child), POINTER :: ctype SELECT TYPE(ctype) CLASS is (parent) CALL do_something(ctype, 0) END SELECT WRITE (*,*) ctype%q END PROGRAM however this still fails. in the select statement it complains that parent must extend child. Im sure this is due to restrictions when dealing with the pointer attribute, for type safety, however, im looking for a way to convert a pointer into its parent type for generic allocation. Rather than have to write separate allocation functions for every type and hope they dont collide in an interface or something. hopefully this example will illustrate a little more clearly what im trying to achieve, if you know a better way let me know

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• Invoking code both before and after WebControl.Render method

  - by Dirk

  I have a set of custom ASP.NET server controls, most of which derive from CompositeControl. I want to implement a uniform look for "required" fields across all control types by wrapping each control in a specific piece of HTML/CSS markup. For example: <div class="requiredInputContainer"> ...custom control markup... </div> I'd love to abstract this behavior in such a way as to avoid having to do something ugly like this in every custom control, present and future: public class MyServerControl : TextBox, IRequirableField { public IRequirableField.IsRequired {get;set;} protected override void Render(HtmlTextWriter writer){ RequiredFieldHelper.RenderBeginTag(this, writer) //render custom control markup RequiredFieldHelper.RenderEndTag(this, writer) } } public static class RequiredFieldHelper{ public static void RenderBeginTag(IRequirableField field, HtmlTextWriter writer){ //check field.IsRequired, render based on its values } public static void RenderEndTag(IRequirableField field, HtmlTextWriter writer){ //check field.IsRequired , render based on its values } } If I was deriving all of my custom controls from the same base class, I could conceivably use Template Method to enforce the before/after behavior;but I have several base classes and I'd rather not end up with really a convoluted class hierarchy anyway. It feels like I should be able to design something more elegant (i.e. adheres to DRY and OCP) by leveraging the functional aspects of C#, but I'm drawing a blank.

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• How can I build a generic dataset-handling Perl library?

  - by Pep.

  Hello, I want to build a generic Perl module for handling and analysing biomedical character separated datasets and which can, most certain, be used on any kind of datasets that contain a mixture of categorical (A,B,C,..) and continuous (1.2,3,881..) and identifier (XXX1,XXX2...). The plan is to have people initialize the module and then use some arguments to point to the data file(s), the place were the analysis reports should be placed and the structure of the data. By structure of data I mean which variable is in which place and its name/type. And this is where I need some enlightenment. I am baffled how to do this in a clean way. Obviously, having people create a simple schema file, be it XML or some other format would be the cleanest but maybe not all people enjoy doing something like this. The solutions I can think of are: Create a configuration file in XML or similar and with a prespecified format. Pass the information during initialization of the module. Use the first row of the data as headers and try to guess types (ouch) Surely there must be a "canonical" way of doing this that is also usable and efficient. Thanks p.

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• How to read from multiple queues in real-world?

  - by Leon Cullens

  Here's a theoretical question: When I'm building an application using message queueing, I'm going to need multiple queues support different data types for different purposes. Let's assume I have 20 queues (e.g. one to create new users, one to process new orders, one to edit user settings, etc.). I'm going to deploy this to Windows Azure using the 'minimum' of 1 web role and 1 worker role. How does one read from all those 20 queues in a proper way? This is what I had in mind, but I have little or no real-world practical experience with this: Create a class that spawns 20 threads in the worker role 'main' class. Let each of these threads execute a method to poll a different queue, and let all those threads sleep between each poll (of course with a back-off mechanism that increases the sleep time). This leads to have 20 threads (or 21?), and 20 queues that are being actively polled, resulting in a lot of wasted messages (each time you poll an empty queue it's being billed as a message). How do you solve this problem?

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• Advice on Minimizing Stored Procedure Parameters

  - by RPM1984

  Hi Guys, I have an ASP.NET MVC Web Application that interacts with a SQL Server 2008 database via Entity Framework 4.0. On a particular page, i call a stored procedure in order to pull back some results based on selections on the UI. Now, the UI has around 20 different input selections, ranging from a textbox, dropdown list, checkboxes, etc. Each of those inputs are "grouped" into logical sections. Example: Search box : "Foo" Checkbox A1: ticked, Checkbox A2: unticked Dropdown A: option 3 selected Checkbox B1: ticked, Checkbox B2: ticked, Checkbox B3: unticked So i need to call the SPROC like this: exec SearchPage_FindResults @SearchQuery = 'Foo', @IncludeA1 = 1, @IncludeA2 = 0, @DropDownSelection = 3, @IncludeB1 = 1, @IncludeB2 = 1, @IncludeB3 = 0 The UI is not too important to this question - just wanted to give some perspective. Essentially, i'm pulling back results for a search query, filtering these results based on a bunch of (optional) selections a user can filter on. Now, My questions/queries: What's the best way to pass these parameters to the stored procedure? Are there any tricks/new ways (e.g SQL Server 2008) to do this? Special "table" parameters/arrays - can we pass through User-Defined-Types? Keep in mind im using Entity Framework 4.0 - but could always use classic ADO.NET for this if required. What about XML? What are the serialization/de-serialization costs here? Is it worth it? How about a parameter for each logical section? Comma-seperated perhaps? Just thinking out loud. This page is particulary important from a user point of view, and needs to perform really well. The stored procedure is already heavy in logic, so i want to minimize the performance implications - so keep that in mind. With that said - what is the best approach here?

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• What's the best way to communicate the purpose of a string parameter in a public API?

  - by Dave

  According to the guidance published in New Recommendations for Using Strings in Microsoft .NET 2.0, the data in a string may exhibit one of the following types of behavior: A non-linguistic identifier, where bytes match exactly. A non-linguistic identifier, where case is irrelevant, especially a piece of data stored in most Microsoft Windows system services. Culturally-agnostic data, which still is linguistically relevant. Data that requires local linguistic customs. Given that, I'd like to know the best way to communicate which behavior is expected of a string parameter in a public API. I wasn't able to find an answer in the Framework Design Guidelines. Consider the following methods: f(string this_is_a_linguistic_string) g(string this_is_a_symbolic_identifier_so_use_ordinal_compares) Is variable naming and XML documentation the best I can do? Could I use attributes in some way to mark the requirements of the string? Now consider the following case: h(Dictionary<string, object> dictionary) Note that the dictionary instance is created by the caller. How do I communicate that the callee expects the IEqualityComparer<string> object held by the dictionary to perform, for example, a case-insensitive ordinal comparison?

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• typeahead.js remote with subset matching

  - by rebelde

  Instead of returning to the server after each additional letter is typed, I want it to only go to the server once, get all matching words, and filter the downloaded data after that. We are having trouble making this work. We are successfully using "remote" to wait until two letters are typed, but we can't get it to stop going to the server as additional letters are typed. Steps: 1. After two letters are typed, retrieve all matching words that start with those two letters. 2. When a third and additional letters are typed, don't go to the server again, just filter from the previous list that was sent. An example: "mo" is typed in. All 100 words that start with "mo" are returned. (Only 10 are shown.) "mor" - now with a third letter, we don't go back to the server. We just find the 20 words that match from within the previous set of words. Can anybody make this work? In real life (using YUI2), we do this and then go back to the server if somebody types in a space after the word. At that point, we know to retrieve additional words. Thanks!

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• How to direct link to an attribute set?

  - by monocat

  I have created attributes; “Shop by Type” and “Shop by Color”. They work great within the layered navigation and extended search. I’ve designed graphics and placed them in the home page and would like to link to the respective attribute’s assigned products. Been searching the webs, but so far have been unsuccessful. If there’s no direct possible way, the next method would be creating cms pages and linking to it directly. How can I display products that are assigned to a specific attribute? Specifically “Multiple Select” types. I know you guys prefer at least some attempts, but as mentioned, been playing with it with no luck. I would appreciate some kind of starting point. Happy Holidays! Edit: I was able to put together this code that lists all the products assigned to said category id. Tried to filter it down where it only displays products that have an assigned same attribute with no luck yet. Any ideas? <?php $cat_id = 123; // category id $category = Mage::getModel('catalog/category')->load($cat_id); $_products = $category->getProductCollection() ->addAttributeToSelect('shop_by_color'); if (($this->getProductCollection()) && $_products->getSize()): ?> By the way, $cat_id is a sub category of root. Is there an easier way to point to it instead of using direct id number?

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