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• C#. Saving information about events and event handlers and removing handlers using this information

  - by Philipp

  I have an object which is creating several event handlers using lambda expressions, and I need to remove all handlers created in that object in one time. I'm trying to create some unified static object which will 'know' which handler relates to which object and event if event handler was created through this static object. I tried something like code below, but I don't understand how to save events and event handlers objects, to be able remove handlers in one time. class Program { static void Main(string[] args) { var EventSender = new EventSender(); var EventReceiver = new EventReceiver(EventSender); EventSender.Invoke(" some var "); LinkSaver.RemoveEvent(EventReceiver); // ?? Console.ReadKey(); } } public class ObjLink{ public object Event; public object Action; } public static class LinkSaver { public static void SetEvent<T>(object obj, Action<T> Event, T Action) { Event(Action); var objLink = new ObjLink{Event = Event, Action = Action}; if (!Links.ContainsKey(obj)) Links.Add(obj, new List<ObjLink>{objLink}); else Links[obj].Add(objLink); } static Dictionary<object,List<ObjLink>> Links = new Dictionary<object, List<ObjLink>>(); public static void RemoveEvent(object obj){ foreach(var objLink in Links[obj]){ // objLink.Event -= objLink.Action; ??? } } } public class EventReceiver { public EventReceiver(EventSender obj) { LinkSaver.SetEvent<EventSender.TestDelegate>(this, obj.SetEvent, str => Console.WriteLine(str + " test event!")); } } public class EventSender { public void Invoke(string var) { if (eventTest != null) eventTest(var); } public void SetEvent(TestDelegate Action) { eventTest += Action; } public delegate void TestDelegate(string var); private event TestDelegate eventTest; // by the way public void RemoveFromEvent() { foreach (var handler in eventTest.GetInvocationList()) eventTest -= (TestDelegate)handler; } }

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• Templates, Function Pointers and C++0x

  - by user328543

  One of my personal experiments to understand some of the C++0x features: I'm trying to pass a function pointer to a template function to execute. Eventually the execution is supposed to happen in a different thread. But with all the different types of functions, I can't get the templates to work. #include `<functional`> int foo(void) {return 2;} class bar { public: int operator() (void) {return 4;}; int something(int a) {return a;}; }; template <class C> int func(C&& c) { //typedef typename std::result_of< C() >::type result_type; typedef typename std::conditional< std::is_pointer< C >::value, std::result_of< C() >::type, std::conditional< std::is_object< C >::value, std::result_of< typename C::operator() >::type, void> >::type result_type; result_type result = c(); return result; } int main(int argc, char* argv[]) { // call with a function pointer func(foo); // call with a member function bar b; func(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); // call with a lambda expression func( [](void)->int {return 12;} ); return 0; } The result_of template alone doesn't seem to be able to find the operator() in class bar and the clunky conditional I created doesn't compile. Any ideas? Will I have additional problems with const functions?

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• LINQ to SQL: NOTing a prebuilt expression

  - by ck

  I'm building a library of functions for one of my core L2S classes, all of which return a bool to allow checking for certain situations. Example: Expression<Func<Account, bool>> IsSomethingX = a => a.AccountSupplementary != null && a.AccountSupplementary.SomethingXFlag != null && a.AccountSupplementary.SomethingXFlag.Value; Now to query where this is not true, I CAN'T do this: var myAccounts= context.Accounts .Where(!IsSomethingX); // does not compile However, using the syntax from the PredicateBuilder class, I've come up with this: public static IQueryable<T> WhereNot<T>(this IQueryable<T> items, Expression<Func<T, bool>> expr1) { var invokedExpr = Expression.Invoke(expr1, expr1.Parameters.Cast<Expression>()); return items.Where(Expression.Lambda<Func<T, bool>> (Expression.Not(invokedExpr), expr1.Parameters)); } var myAccounts= context.Accounts .WhereNot(IsSomethingX); // does compile which actually produces the correct SQL. Does this look like a good solution, and is there anything I need to be aware of that might cause me problems in future?

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• Reordering fields in Django model

  - by Alex Lebedev

  I want to add few fields to every model in my django application. This time it's created_at, updated_at and notes. Duplicating code for every of 20+ models seems dumb. So, I decided to use abstract base class which would add these fields. The problem is that fields inherited from abstract base class come first in the field list in admin. Declaring field order for every ModelAdmin class is not an option, it's even more duplicate code than with manual field declaration. In my final solution, I modified model constructor to reorder fields in _meta before creating new instance: class MyModel(models.Model): # Service fields notes = my_fields.NotesField() created_at = models.DateTimeField(auto_now_add=True) updated_at = models.DateTimeField(auto_now=True) class Meta: abstract = True last_fields = ("notes", "created_at", "updated_at") def __init__(self, *args, **kwargs): new_order = [f.name for f in self._meta.fields] for field in self.last_fields: new_order.remove(field) new_order.append(field) self._meta._field_name_cache.sort(key=lambda x: new_order.index(x.name)) super(TwangooModel, self).__init__(*args, **kwargs) class ModelA(MyModel): field1 = models.CharField() field2 = models.CharField() #etc ... It works as intended, but I'm wondering, is there a better way to acheive my goal?

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• STI and accepts_nested_attributes_for in rails

  - by ryanshackintosh

  I have models as follows: class Entity < ActiveRecord::Base has_many :addresses accepts_nested_attributes_for :addresses, :reject_if => lambda { |a| a[:label].blank?} , :allow_destroy => true end class Client < Entity before_save :set_type private def set_type self.type = "Client" end end class Address < ActiveRecord::Base belongs_to :entity end I have recently implemented accepts_nested_attributes_for on the /clients/new form, as follows: <% form_for(@client, :html => {:class => 'form'}) do |f| -%> <%= f.label :name %> <%= f.text_field :name -%> <%= f.label :phone %> <%= f.text_field :phone %> <% f.fields_for :addresses do |a| %> <%= a.label :street %> <%= a.text_field :street%> <%= a.label :city %> <%= a.text_field :city %> <% end %> <% end %> And my controller as follows: class ClientsController < ApplicationController before_filter :load_client , :except => [:index, :new, :create, :render_clients] def new @client = Client.new @client.addresses.build end def create @client = Client.new(params[:client]) if @client.save flash[:notice] = 'Client has been successfully added' redirect_to @client else render :action => 'new' end end The issue is that when the record is saved it gives an error stating: "Entity can't be blank" I assume it is something to do with the fact that a 'Client' and not an 'Entity' is being added. Can anyone point me in the right direction?

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• Syntax errors on Heroku, but not on local server (postgresql related?)

  - by Phil_Ken_Sebben

  I'm trying to deploy my first app on Heroku (rails 3). It works fine on my local server, but when I pushed it to Heroku and ran it, it crashes, giving a number of syntax errors. These are related to a collection of scopes I use like the one below: scope :scored, lambda { |score = nil| score.nil? ? {} : where('products.votes_count >= ?', score) } it produces errors of this form: "syntax error, unexpected '=', expecting '|' " "syntax error, unexpected '}', expecting kEND" Why is this syntax making Heroku choke and how can I correct it? Thanks! EDIT: I was using sqlite on my local machine and Heroku does not support that. Trying to make sure the db is properly configured for PG. I believe I have done that by specifying in the gemfile that sqlite only be used in development. Yet I still get these syntax errors, that interrupt even the db:migrate. EDIT: So now it seems more likely that my scope syntax doesn't work in postgreSQL. Does anyone know how to convert this properly?

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• Making Extension method Generic

  - by Ian

  In this post there's a very interesting way of updating UI threads using a static extension method. public static void InvokeIfRequired(this Control c, Action<Control> action) { if(c.InvokeRequired) { c.Invoke(() => action(c)); } else { action(c); } } What I want to do, is to make a generic version, so I'm not constrained by a control. This would allow me to do the following for example (because I'm no longer constrained to just being a Control) this.progressBar1.InvokeIfRequired(pb => pb.Value = e.Progress); I've tried the following: public static void InvokeIfRequired<T>(this T c, Action<T> action) where T : Control { if (c.InvokeRequired) { c.Invoke(() => action(c)); } else { action(c); } } But I get the following error that I'm not sure how to fix. Anyone any suggestions? Error 5 Cannot convert lambda expression to type 'System.Delegate' because it is not a delegate type

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• Nested bind expressions

  - by user328543

  This is a followup question to my previous question. #include <functional> int foo(void) {return 2;} class bar { public: int operator() (void) {return 3;}; int something(int a) {return a;}; }; template <class C> auto func(C&& c) -> decltype(c()) { return c(); } template <class C> int doit(C&& c) { return c();} template <class C> void func_wrapper(C&& c) { func( std::bind(doit<C>, std::forward<C>(c)) ); } int main(int argc, char* argv[]) { // call with a function pointer func(foo); func_wrapper(foo); // error // call with a member function bar b; func(b); func_wrapper(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); func_wrapper(std::bind(&bar::something, b, 42)); // error // call with a lambda expression func( [](void)->int {return 42;} ); func_wrapper( [](void)->int {return 42;} ); return 0; } I'm getting a compile errors deep in the C++ headers: functional:1137: error: invalid initialization of reference of type ‘int (&)()’ from expression of type ‘int (*)()’ functional:1137: error: conversion from ‘int’ to non-scalar type ‘std::_Bind(bar, int)’ requested func_wrapper(foo) is supposed to execute func(doit(foo)). In the real code it packages the function for a thread to execute. func would the function executed by the other thread, doit sits in between to check for unhandled exceptions and to clean up. But the additional bind in func_wrapper messes things up...

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• Is there an alias for 'this' in TypeScript?

  - by Todd

  I've attempted to write a class in TypeScript that has a method defined which acts as an event handler callback to a jQuery event. class Editor { textarea: JQuery; constructor(public id: string) { this.textarea = $(id); this.textarea.focusin(onFocusIn); } onFocusIn(e: JQueryEventObject) { var height = this.textarea.css('height'); // <-- This is not good. } } Within the onFocusIn event handler, TypeScript sees 'this' as being the 'this' of the class. However, jQuery overrides the this reference and sets it to the DOM object associated with the event. One alternative is to define a lambda within the constructor as the event handler, in which case TypeScript creates a sort of closure with a hidden _this alias. class Editor { textarea: JQuery; constructor(public id: string) { this.textarea = $(id); this.textarea.focusin((e) => { var height = this.textarea.css('height'); // <-- This is good. }); } } My question is, is there another way to access the this reference within the method-based event handler using TypeScript, to overcome this jQuery behavior?

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• Effective simulation of compound poisson process in Matlab

  - by Henrik

  I need to simulate a huge bunch of compound poisson processes in Matlab on a very fine grid so I am looking to do it most effectively. I need to do a lot of simulations on the same random numbers but with parameters changing so it is practical to draw the uniforms and normals beforehand even though it means i have to draw a lot more than i will probably need and won't matter much because it will only need to be done once compared to in the order 500*n repl times the actual compound process generation. My method is the following: Let T be for how long i need to simulate and N the grid points, then my grid is: t=linspace(1,T,N); Let nrepl be the number of processes i need then I simulate P=poissrnd(lambda,nrepl,1); % Number of jumps for each replication U=(T-1)*rand(10000,nrepl)+1; % Set of uniforms on (1,T) for jump times N=randn(10000,nrepl); % Set of normals for jump size Then for replication j: Poiss=P(j); % Jumps for replication Uni=U(1:Poiss,j);% Jump times Norm=mu+sigma*N(1:Poiss,j);% Jump sizes Then this I guess is where I need your advice, I use this one-liner but it seems very slow: CPP_norm=sum(bsxfun(@times,bsxfun(@gt,t,Uni),Norm),1); In the inner for each jump it creates a series of same length as t with 0 until jump and then 1 after, multiplying this will create a grid with zeroes until jump has arrived and then the jump size and finally adding all these will produce the entire jump process on the grid. How can this be done more effectively? Thank you very much.

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• Dynamic programming Approach- Knapsack Puzzle

  - by idalsin

  I'm trying to solve the Knapsack problem with the dynamical programming(DP) approach, with Python 3.x. My TA pointed us towards this code for a head start. I've tried to implement it, as below: def take_input(infile): f_open = open(infile, 'r') lines = [] for line in f_open: lines.append(line.strip()) f_open.close() return lines def create_list(jewel_lines): #turns the jewels into a list of lists jewels_list = [] for x in jewel_lines: weight = x.split()[0] value = x.split()[1] jewels_list.append((int(value), int(weight))) jewels_list = sorted(jewels_list, key = lambda x : (-x[0], x[1])) return jewels_list def dynamic_grab(items, max_weight): table = [[0 for weight in range(max_weight+1)] for j in range(len(items)+1)] for j in range(1,len(items)+1): val= items[j-1][0] wt= items[j-1][1] for weight in range(1, max_weight+1): if wt > weight: table[j][weight] = table[j-1][weight] else: table[j][weight] = max(table[j-1][weight],table[j-1][weight-wt] + val) result = [] weight = max_weight for j in range(len(items),0,-1): was_added = table[j][weight] != table[j-1][weight] if was_added: val = items[j-1][0] wt = items[j-1][1] result.append(items[j-1]) weight -= wt return result def totalvalue(comb): #total of a combo of items totwt = totval = 0 for val, wt in comb: totwt += wt totval += val return (totval, -totwt) if totwt <= max_weight else (0,0) #required setup of variables infile = "JT_test1.txt" given_input = take_input(infile) max_weight = int(given_input[0]) given_input.pop(0) jewels_list = create_list(given_input) #test lines print(jewels_list) print(greedy_grab(jewels_list, max_weight)) bagged = dynamic_grab(jewels_list, max_weight) print(totalvalue(bagged)) The sample case is below. It is in the format line[0] = bag_max, line[1:] is in form(weight, value): 575 125 3000 50 100 500 6000 25 30 I'm confused as to the logic of this code in that it returns me a tuple and I'm not sure what the output tuple represents. I've been looking at this for a while and just don't understand what the code is pointing me at. Any help would be appreciated.

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• Parallelism in .NET – Part 17, Think Continuations, not Callbacks

  - by Reed

  In traditional asynchronous programming, we’d often use a callback to handle notification of a background task’s completion.  The Task class in the Task Parallel Library introduces a cleaner alternative to the traditional callback: continuation tasks. Asynchronous programming methods typically required callback functions.  For example, MSDN’s Asynchronous Delegates Programming Sample shows a class that factorizes a number.  The original method in the example has the following signature: public static bool Factorize(int number, ref int primefactor1, ref int primefactor2) { //... .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } However, calling this is quite “tricky”, even if we modernize the sample to use lambda expressions via C# 3.0.  Normally, we could call this method like so: int primeFactor1 = 0; int primeFactor2 = 0; bool answer = Factorize(10298312, ref primeFactor1, ref primeFactor2); Console.WriteLine("{0}/{1} [Succeeded {2}]", primeFactor1, primeFactor2, answer); If we want to make this operation run in the background, and report to the console via a callback, things get tricker.  First, we need a delegate definition: public delegate bool AsyncFactorCaller( int number, ref int primefactor1, ref int primefactor2); Then we need to use BeginInvoke to run this method asynchronously: int primeFactor1 = 0; int primeFactor2 = 0; AsyncFactorCaller caller = new AsyncFactorCaller(Factorize); caller.BeginInvoke(10298312, ref primeFactor1, ref primeFactor2, result => { int factor1 = 0; int factor2 = 0; bool answer = caller.EndInvoke(ref factor1, ref factor2, result); Console.WriteLine("{0}/{1} [Succeeded {2}]", factor1, factor2, answer); }, null); This works, but is quite difficult to understand from a conceptual standpoint.  To combat this, the framework added the Event-based Asynchronous Pattern, but it isn’t much easier to understand or author. Using .NET 4’s new Task<T> class and a continuation, we can dramatically simplify the implementation of the above code, as well as make it much more understandable.  We do this via the Task.ContinueWith method.  This method will schedule a new Task upon completion of the original task, and provide the original Task (including its Result if it’s a Task<T>) as an argument.  Using Task, we can eliminate the delegate, and rewrite this code like so: var background = Task.Factory.StartNew( () => { int primeFactor1 = 0; int primeFactor2 = 0; bool result = Factorize(10298312, ref primeFactor1, ref primeFactor2); return new { Result = result, Factor1 = primeFactor1, Factor2 = primeFactor2 }; }); background.ContinueWith(task => Console.WriteLine("{0}/{1} [Succeeded {2}]", task.Result.Factor1, task.Result.Factor2, task.Result.Result)); This is much simpler to understand, in my opinion.  Here, we’re explicitly asking to start a new task, then continue the task with a resulting task.  In our case, our method used ref parameters (this was from the MSDN Sample), so there is a little bit of extra boiler plate involved, but the code is at least easy to understand. That being said, this isn’t dramatically shorter when compared with our C# 3 port of the MSDN code above.  However, if we were to extend our requirements a bit, we can start to see more advantages to the Task based approach.  For example, supposed we need to report the results in a user interface control instead of reporting it to the Console.  This would be a common operation, but now, we have to think about marshaling our calls back to the user interface.  This is probably going to require calling Control.Invoke or Dispatcher.Invoke within our callback, forcing us to specify a delegate within the delegate.  The maintainability and ease of understanding drops.  However, just as a standard Task can be created with a TaskScheduler that uses the UI synchronization context, so too can we continue a task with a specific context.  There are Task.ContinueWith method overloads which allow you to provide a TaskScheduler.  This means you can schedule the continuation to run on the UI thread, by simply doing: Task.Factory.StartNew( () => { int primeFactor1 = 0; int primeFactor2 = 0; bool result = Factorize(10298312, ref primeFactor1, ref primeFactor2); return new { Result = result, Factor1 = primeFactor1, Factor2 = primeFactor2 }; }).ContinueWith(task => textBox1.Text = string.Format("{0}/{1} [Succeeded {2}]", task.Result.Factor1, task.Result.Factor2, task.Result.Result), TaskScheduler.FromCurrentSynchronizationContext()); This is far more understandable than the alternative.  By using Task.ContinueWith in conjunction with TaskScheduler.FromCurrentSynchronizationContext(), we get a simple way to push any work onto a background thread, and update the user interface on the proper UI thread.  This technique works with Windows Presentation Foundation as well as Windows Forms, with no change in methodology.

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• CLR via C# 3rd Edition is out

  - by Abhijeet Patel

  Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

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• LINQ und ArcObjects

  - by Marko Apfel

  LINQ und ArcObjects Motivation LINQ1 (language integrated query) ist eine Komponente des Microsoft .NET Frameworks seit der Version 3.5. Es erlaubt eine SQL-ähnliche Abfrage zu verschiedenen Datenquellen wie SQL, XML u.v.m. Wie SQL auch, bietet LINQ dazu eine deklarative Notation der Problemlösung - d.h. man muss nicht im Detail beschreiben wie eine Aufgabe, sondern was überhaupt zu lösen ist. Das befreit den Entwickler abfrageseitig von fehleranfälligen Iterator-Konstrukten. Ideal wäre es natürlich auf diese Möglichkeiten auch in der ArcObjects-Programmierung mit Features zugreifen zu können. Denkbar wäre dann folgendes Konstrukt: var largeFeatures = from feature in features where (feature.GetValue("SHAPE_Area").ToDouble() > 3000) select feature; bzw. dessen Äquivalent als Lambda-Expression: var largeFeatures = features.Where(feature => (feature.GetValue("SHAPE_Area").ToDouble() > 3000)); Dazu muss ein entsprechender Provider zu Verfügung stehen, der die entsprechende Iterator-Logik managt. Dies ist leichter als man auf den ersten Blick denkt - man muss nur die gewünschten Entitäten als IEnumerable<IFeature> liefern. (Anm.: nicht wundern - die Methoden GetValue() und ToDouble() habe ich nebenbei als Erweiterungsmethoden deklariert.) Im Hintergrund baut LINQ selbständig eine Zustandsmaschine (state machine)2 auf deren Ausführung verzögert ist (deferred execution)3 - d.h. dass erst beim tatsächlichen Anfordern von Entitäten (foreach, Count(), ToList(), ..) eine Instanziierung und Verarbeitung stattfindet, obwohl die Zuweisung schon an ganz anderer Stelle erfolgte. Insbesondere bei mehrfacher Iteration durch die Entitäten reibt man sich bei den ersten Debuggings verwundert die Augen wenn der Ausführungszeiger wie von Geisterhand wieder in die Iterator-Logik springt. Realisierung Eine ganz knappe Logik zum Konstruieren von IEnumerable<IFeature> lässt sich mittels Durchlaufen eines IFeatureCursor realisieren. Dazu werden die einzelnen Feature mit yield ausgegeben. Der einfachen Verwendung wegen, habe ich die Logik in eine Erweiterungsmethode GetFeatures() für IFeatureClass aufgenommen: public static IEnumerable GetFeatures(this IFeatureClass featureClass, IQueryFilter queryFilter, RecyclingPolicy policy) { IFeatureCursor featureCursor = featureClass.Search(queryFilter, RecyclingPolicy.Recycle == policy); IFeature feature; while (null != (feature = featureCursor.NextFeature())) { yield return feature; } //this is skipped in unit tests with cursor-mock if (Marshal.IsComObject(featureCursor)) { Marshal.ReleaseComObject(featureCursor); } } Damit kann man sich nun ganz einfach die IEnumerable<IFeature> erzeugen lassen: IEnumerable features = _featureClass.GetFeatures(RecyclingPolicy.DoNotRecycle); Etwas aufpassen muss man bei der Verwendung des "Recycling-Cursors". Nach einer verzögerten Ausführung darf im selben Kontext nicht erneut über die Features iteriert werden. In diesem Fall wird nämlich nur noch der Inhalt des letzten (recycelten) Features geliefert und alle Features sind innerhalb der Menge gleich. Kritisch würde daher das Konstrukt largeFeatures.ToList(). ForEach(feature => Debug.WriteLine(feature.OID)); weil ToList() schon einmal durch die Liste iteriert und der Cursor somit einmal durch die Features bewegt wurde. Die Erweiterungsmethode ForEach liefert dann immer dasselbe Feature. In derartigen Situationen darf also kein Cursor mit Recycling verwendet werden. Ein mehrfaches Ausführen von foreach ist hingegen kein Problem weil dafür jedes Mal die Zustandsmaschine neu instanziiert wird und somit der Cursor neu durchlaufen wird – das ist die oben schon erwähnte Magie. Ausblick Nun kann man auch einen Schritt weiter gehen und ganz eigene Implementierungen für die Schnittstelle IEnumerable<IFeature> in Angriff nehmen. Dazu müssen nur die Methode und das Property zum Zugriff auf den Enumerator ausprogrammiert werden. Im Enumerator selbst veranlasst man in der Reset()-Methode das erneute Ausführen der Suche – dazu übergibt man beispielsweise ein entsprechendes Delegate in den Konstruktur: new FeatureEnumerator( _featureClass, featureClass => featureClass.Search(_filter, isRecyclingCursor)); und ruft dieses beim Reset auf: public void Reset() {     _featureCursor = _resetCursor(_t); } Auf diese Art und Weise können Enumeratoren für völlig verschiedene Szenarien implementiert werden, die clientseitig restlos identisch nach obigen Schema verwendet werden. Damit verschmelzen Cursors, SelectionSets u.s.w. zu einer einzigen Materie und die Wiederverwendbarkeit von Code steigt immens. Obendrein lässt sich ein IEnumerable in automatisierten Unit-Tests sehr einfach mocken - ein großer Schritt in Richtung höherer Software-Qualität.4 Fazit Nichtsdestotrotz ist Vorsicht mit diesen Konstrukten in performance-relevante Abfragen geboten. Dadurch dass im Hintergrund eine Zustandsmaschine verwalten wird, entsteht einiges an Overhead dessen Verarbeitung zusätzliche Zeit kostet - ca. 20 bis 100 Prozent. Darüber hinaus ist auch das Arbeiten ohne Recycling schnell ein Performance-Gap. Allerdings ist deklarativer LINQ-Code viel eleganter, fehlerfreier und wartungsfreundlicher als das manuelle Iterieren, Vergleichen und Aufbauen einer Ergebnisliste. Der Code-Umfang verringert sich erfahrungsgemäß im Schnitt um 75 bis 90 Prozent! Dafür warte ich gerne ein paar Millisekunden länger. Wie so oft muss abgewogen werden zwischen Wartbarkeit und Performance - wobei für mich Wartbarkeit zunehmend an Priorität gewinnt. Zumeist ist sowieso nicht der Code sondern der Anwender die Bremse im Prozess. Demo-Quellcode support.esri.de   [1] Wikipedia: LINQ http://de.wikipedia.org/wiki/LINQ [2] Wikipedia: Zustandsmaschine http://de.wikipedia.org/wiki/Endlicher_Automat [3] Charlie Calverts Blog: LINQ and Deferred Execution http://blogs.msdn.com/b/charlie/archive/2007/12/09/deferred-execution.aspx [4] Clean Code Developer - gelber Grad/Automatisierte Unit Tests http://www.clean-code-developer.de/Gelber-Grad.ashx#Automatisierte_Unit_Tests_8

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• Write your Tests in RSpec with IronRuby

  - by kazimanzurrashid

  [Note: This is not a continuation of my previous post, treat it as an experiment out in the wild. ] Lets consider the following class, a fictitious Fund Transfer Service: public class FundTransferService : IFundTransferService { private readonly ICurrencyConvertionService currencyConvertionService; public FundTransferService(ICurrencyConvertionService currencyConvertionService) { this.currencyConvertionService = currencyConvertionService; } public void Transfer(Account fromAccount, Account toAccount, decimal amount) { decimal convertionRate = currencyConvertionService.GetConvertionRate(fromAccount.Currency, toAccount.Currency); decimal convertedAmount = convertionRate * amount; fromAccount.Withdraw(amount); toAccount.Deposit(convertedAmount); } } public class Account { public Account(string currency, decimal balance) { Currency = currency; Balance = balance; } public string Currency { get; private set; } public decimal Balance { get; private set; } public void Deposit(decimal amount) { Balance += amount; } public void Withdraw(decimal amount) { Balance -= amount; } } We can write the spec with MSpec + Moq like the following: public class When_fund_is_transferred { const decimal ConvertionRate = 1.029m; const decimal TransferAmount = 10.0m; const decimal InitialBalance = 100.0m; static Account fromAccount; static Account toAccount; static FundTransferService fundTransferService; Establish context = () => { fromAccount = new Account("USD", InitialBalance); toAccount = new Account("CAD", InitialBalance); var currencyConvertionService = new Moq.Mock<ICurrencyConvertionService>(); currencyConvertionService.Setup(ccv => ccv.GetConvertionRate(Moq.It.IsAny<string>(), Moq.It.IsAny<string>())).Returns(ConvertionRate); fundTransferService = new FundTransferService(currencyConvertionService.Object); }; Because of = () => { fundTransferService.Transfer(fromAccount, toAccount, TransferAmount); }; It should_decrease_from_account_balance = () => { fromAccount.Balance.ShouldBeLessThan(InitialBalance); }; It should_increase_to_account_balance = () => { toAccount.Balance.ShouldBeGreaterThan(InitialBalance); }; } and if you run the spec it will give you a nice little output like the following: When fund is transferred » should decrease from account balance » should increase to account balance 2 passed, 0 failed, 0 skipped, took 1.14 seconds (MSpec). Now, lets see how we can write exact spec in RSpec. require File.dirname(__FILE__) + "/../FundTransfer/bin/Debug/FundTransfer" require "spec" require "caricature" describe "When fund is transferred" do Convertion_Rate = 1.029 Transfer_Amount = 10.0 Initial_Balance = 100.0 before(:all) do @from_account = FundTransfer::Account.new("USD", Initial_Balance) @to_account = FundTransfer::Account.new("CAD", Initial_Balance) currency_convertion_service = Caricature::Isolation.for(FundTransfer::ICurrencyConvertionService) currency_convertion_service.when_receiving(:get_convertion_rate).with(:any, :any).return(Convertion_Rate) fund_transfer_service = FundTransfer::FundTransferService.new(currency_convertion_service) fund_transfer_service.transfer(@from_account, @to_account, Transfer_Amount) end it "should decrease from account balance" do @from_account.balance.should be < Initial_Balance end it "should increase to account balance" do @to_account.balance.should be > Initial_Balance end end I think the above code is self explanatory, treat the require(line 1- 4) statements as the add reference of our visual studio projects, we are adding all the required libraries with this statement. Next, the describe which is a RSpec keyword. The before does exactly the same as NUnit's Setup or MsTest’s TestInitialize attribute, but in the above we are using before(:all) which acts as ClassInitialize of MsTest, that means it will be executed only once before all the test methods. In the before(:all) we are first instantiating the from and to accounts, it is same as creating with the full name (including namespace)  like fromAccount = new FundTransfer.Account(.., ..), next, we are creating a mock object of ICurrencyConvertionService, check that for creating the mock we are not using the Moq like the MSpec version. This is somewhat an interesting issue of IronRuby or maybe the DLR, it seems that it is not possible to use the lambda expression that most of the mocking tools uses in arrange phase in Iron Ruby, like: currencyConvertionService.Setup(ccv => ccv.GetConvertionRate(Moq.It.IsAny<string>(), Moq.It.IsAny<string>())).Returns(ConvertionRate); But the good news is, there is already an excellent mocking tool called Caricature written completely in IronRuby which we can use to mock the .NET classes. May be all the mocking tool providers should give some thought to add the support for the DLR, so that we can use the tool that we are already familiar with. I think the rest of the code is too simple, so I am skipping the explanation. Now, the last thing, how we are going to run it with RSpec, lets first install the required gems. Open you command prompt and type the following: igem sources -a http://gems.github.com This will add the GitHub as gem source. Next type: igem install uuidtools caricature rspec and at last we have to create a batch file so that we can execute it in the Notepad++, create a batch like in the IronRuby bin directory like my previous post and put the following in that batch file: @echo off cls call spec %1 --format specdoc pause Next, add a run menu and shortcut in the Notepad++ like my previous post. Now when we run it it will show the following output: When fund is transferred - should decrease from account balance - should increase to account balance Finished in 0.332042 seconds 2 examples, 0 failures Press any key to continue . . . You will complete code of this post in the bottom. That's it for today. Download: RSpecIntegration.zip

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• So what are zones really?

  - by Bertrand Le Roy

  There is a (not so) particular kind of shape in Orchard: zones. Functionally, zones are places where other shapes can render. There are top-level zones, the ones defined on Layout, where widgets typically go, and there are local zones that can be defined anywhere. These local zones are what you target in placement.info. Creating a zone is easy because it really is just an empty shape. Most themes include a helper for it: Func<dynamic, dynamic> Zone = x => Display(x); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } With this helper, you can create a zone by simply writing: @Zone(Model.Header) .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Let's deconstruct what's happening here with that weird Lambda. In the Layout template where we are working, the Model is the Layout shape itself, so Model.Header is really creating a new Header shape under Layout, or getting a reference to it if it already exists. The Zone function is then called on that object, which is equivalent to calling Display. In other words, you could have just written the following to get the exact same effect: @Display(Model.Header) The Zone helper function only exists to make the intent very explicit. Now here's something interesting: while this works in the Layout template, you can also make it work from any deeper-nested template and still create top-level zones. The difference is that wherever you are, Model is not the layout anymore so you need to access it in a different way: @Display(WorkContext.Layout.Header) This is still doing the exact same thing as above. One thing to know is that for top-level zones to be usable from the widget editing UI, you need one more thing, which is to specify it in the theme's manifest: Name: Contoso Author: The Orchard Team Description: A subtle and simple CMS themeVersion: 1.1 Tags: business, cms, modern, simple, subtle, product, service Website: http://www.orchardproject.net Zones: Header, Navigation, HomeFeaturedImage, HomeFeaturedHeadline, Messages, Content, ContentAside, TripelFirst, TripelSecond, TripelThird, Footer Local zones are just ordinary shapes like global zones, the only difference being that they are created on a deeper shape than layout. For example, in Content.cshtml, you can find our good old code fro creating a header zone: @Display(Model.Header) The difference here is that Model is no longer the Layout shape, so that zone will be local. The name of that local zone is what you specify in placement.info, for example: <Place Parts_Common_Metadata_Summary="Header:1"/> Now here's the really interesting part: zones do not even know that they are zones, and in fact any shape can be substituted. That means that if you want to add new shapes to the shape that some part has been emitting from its driver for example, you can absolutely do that. And because zones are so barebones as shapes go, they can be created the first time they are accessed. This is what enables us to add shapes into a zone before the code that you would think creates it has even run. For example, in the Layout.cshtml template in TheThemeMachine, the BadgeOfHonor shape is being injected into the Footer zone on line 47, even though that zone will really be "created" on line 168.

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• Introducing jLight &ndash; Talking to the DOM using Silverlight and jQuery.

  - by Timmy Kokke

  Introduction With the recent news about Silverlight on the Windows Phone and all the great Out-Of-Browser features in the upcoming Silverlight 4 you almost forget Silverlight is a browser plugin. It most often runs in a web browser and often as a control. In many cases you need to communicate with the browser to get information about textboxes, events or details about the browser itself. To do this you can use JavaScript from Silverlight. Although Silverlight works the same on every browser, JavaScript does not and it won’t be long before problems arise. To overcome differences in browser I like to use jQuery. The only downside of doing this is that there’s a lot more code needed that you would normally use when you write jQuery in JavaScript. Lately, I had to catch changes is the browser scrollbar and act to the new position. I also had to move the scrollbar when the user dragged around in the Silverlight application. With jQuery it was peanuts to get and set the right attributes, but I found that I had to write a lot of code on Silverlight side.  With a few refactoring I had a separated out the plumbing into a new class and could call only a few methods on that to get the same thing done. The idea for jLight was born. jLight vs. jQuery The main purpose of jLight is to take the ease of use of jQuery and bring it into Silverlight for handling DOM interaction. For example, to change the text color of a DIV to red, in jQuery you would write: jQuery("div").css("color","red"); In jLight the same thing looks like so: jQuery.Select("div").Css("color","red");   Another example. To change the offset in of the last SPAN you could write this in jQuery : jQuery("span:last").offset({left : 10, top : 100});   In jLight this would do the same: jQuery.Select("span:last").Offset(new {left = 10, top = 100 });   Callbacks Nothing too special so far. To get the same thing done using the “normal” HtmlPage.Window.Eval, it wouldn’t require too much effort. But to wire up a handler for events from the browser it’s a whole different story. Normally you need to register ScriptMembers, ScriptableTypes or write some code in JavaScript. jLight takes care of the plumbing and provide you with an simple interface in the same way jQuery would. If you would like to handle the scroll event of the BODY of your html page, you’ll have to bind the event using jQuery and have a function call back to a registered function in Silverlight. In the example below I assume there’s a method “SomeMethod” and it is registered as a ScriptableObject as “RegisteredFromSilverlight” from Silverlight.   jQuery("body:first").scroll(function() { var sl = document.getElementbyId("SilverlightControl"); sl.content.RegisteredFromSilverlight.SomeMethod($(this)); });       Using jLight  in Silverlight the code would be even simpler. The registration of RegisteredFromSilverlight  as ScriptableObject can be omitted.  Besides that, you don’t have to write any JavaScript or evaluate strings with JavaScript.   jQuery.Select("body:first").scroll(SomeMethod);   Lambdas Using a lambda in Silverlight can make it even simpler.  Each is the jQuery equivalent of foreach in C#. It calls a function for every element found by jQuery. In this example all INPUT elements of the text type are selected. The FromObject method is used to create a jQueryObject from an object containing a ScriptObject. The Val method from jQuery is used to get the value of the INPUT elements.   jQuery.Select("input:text").Each((element, index) => { textBox1.Text += jQueryObject.FromObject(element).Val(); return null; });   Ajax One thing jQuery is often used for is making Ajax calls. Making calls to services to external services can be done from Silverlight, but as easy as using jQuery. As an example I would like to show how jLight does this. Below is the entire code behind. It searches my name on twitter and shows the result. This example can be found in the source of the project. The GetJson method passes a Silverlight JsonValue to a callback. This callback instantiates Twit objects and adds them to a ListBox called TwitList.   public partial class DemoPage2 : UserControl { public DemoPage2() { InitializeComponent(); jQuery.Load(); }   private void CallButton_Click(object sender, RoutedEventArgs e) { jQuery.GetJson("http://search.twitter.com/search.json?lang=en&q=sorskoot", Done); }   private void Done(JsonValue arg) { var tweets = new List<Twit>(); foreach (JsonObject result in arg["results"]) { tweets.Add(new Twit() { Text = (string)result["text"], Image = (string)result["profile_image_url"], User = (string)result["from_user"] } ); } TwitList.ItemsSource = tweets; } }   public class Twit { public string User { get; set; } public string Image { get; set; } public string Text { get; set; } }   Conclusion Although jLight is still in development it can be used already.There isn’t much documentation yet, but if you know jQuery jLight isn’t very hard to use.  If you would like to try it, please let me know what you think and report any problems you run in to. jLight can be found at:   http://jlight.codeplex.com

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• Blog Buzz - Devoxx 2011

  - by Janice J. Heiss

  Some day I will make it to Devoxx – for now, I’m content to vicariously follow the blogs of attendees and pick up on what’s happening.  I’ve been doing more blog "fishing," looking for the best commentary on 2011 Devoxx. There’s plenty of food for thought – and the ideas are not half-baked.The bloggers are out in full, offering useful summaries and commentary on Devoxx goings-on.Constantin Partac, a Java developer and a member of Transylvania JUG, a community from Cluj-Napoca/Romania, offers an excellent summary of the Devoxx keynotes. Here’s a sample:“Oracle Opening Keynote and JDK 7, 8, and 9 Presentation•    Oracle is committed to Java and wants to provide support for it on any device.•    JSE 7 for Mac will be released next week.•    Oracle would like Java developers to be involved in JCP, to adopt a JSR and to attend local JUG meetings.•    JEE 7 will be released next year.•    JEE 7 is focused on cloud integration, some of the features are already implemented in glassfish 4 development branch.•    JSE 8 will be release in summer of 2013 due to “enterprise community request” as they can not keep the pace with an 18    month release cycle.•    The main features included in JSE8 are lambda support, project Jigsaw, new Date/Time API, project Coin++ and adding   support for sensors. JSE 9 probably will focus on some of these features:1.    self tuning JVM2.    improved native language integration3.    processing enhancement for big data4.    reification (adding runtime class type info for generic types)5.    unification of primitive and corresponding object classes6.    meta-object protocol in order to use type and methods define in other JVM languages7.    multi-tenancy8.    JVM resource management” Thanks Constantin! Ivan St. Ivanov, of SAP Labs Bulgaria, also commented on the keynotes with a different focus.  He summarizes Henrik Stahl’s look ahead to Java SE 8 and JavaFX 3.0; Cameron Purdy on Java EE and the cloud; celebrated Java Champion Josh Bloch on what’s good and bad about Java; Mark Reinhold’s quick look ahead to Java SE 9; and Brian Goetz on lambdas and default methods in Java SE 8. Here’s St. Ivanov’s account of Josh Bloch’s comments on the pluses of Java:“He started with the virtues of the platform. To name a few:    Tightly specified language primitives and evaluation order – int is always 32 bits and operations are executed always from left  to right, without compilers messing around    Dynamic linking – when you change a class, you need to recompile and rebuild just the jar that has it and not the whole application    Syntax  similarity with C/C++ – most existing developers at that time felt like at home    Object orientations – it was cool at that time as well as functional programming is today    It was statically typed language – helps in faster runtime, better IDE support, etc.    No operator overloading – well, I’m not sure why it is good. Scala has it for example and that’s why it is far better for defining DSLs. But I will not argue with Josh.”It’s worth checking out St. Ivanov’s summary of Bloch’s views on what’s not so great about Java as well. What's Coming in JAX-RS 2.0Marek Potociar, Principal Software Engineer at Oracle and currently specification lead of Java EE RESTful web services API (JAX-RS), blogged on his talk about what's coming in JAX-RS 2.0, scheduled for final release in mid-2012.  Here’s a taste:“Perhaps the most wanted addition to the JAX-RS is the Client API, that would complete the JAX-RS story, that is currently server-side only. In JAX-RS 2.0 we are adding a completely interface-based and fluent client API that blends nicely in with the existing fluent response builder pattern on the server-side. When we started with the client API, the first proposal contained around 30 classes. Thanks to the feedback from our Expert Group we managed to reduce the number of API classes to 14 (2 of them being exceptions)! The resulting is compact while at the same time we still managed to create an API that reflects the method invocation context flow (e.g. once you decide on the target URI and start setting headers on the request, your IDE will not try to offer you a URI setter in the code completion). This is a subtle but very important usability aspect of an API…” Obviously, Devoxx is a great Java conference, one that is hitting this year at a time when much is brewing in the platform and beginning to be anticipated.

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• Using a Predicate as a key to a Dictionary

  - by Tom Hines

  I really love Linq and Lambda Expressions in C#.  I also love certain community forums and programming websites like DaniWeb. A user on DaniWeb posted a question about comparing the results of a game that is like poker (5-card stud), but is played with dice. The question stemmed around determining what was the winning hand.  I looked at the question and issued some comments and suggestions toward a potential answer, but I thought it was a neat homework exercise. [A little explanation] I eventually realized not only could I compare the results of the hands (by name) with a certain construct – I could also compare the values of the individual dice with the same construct. That piece of code eventually became a Dictionary with the KEY as a Predicate<int> and the Value a Func<T> that returns a string from the another structure that contains the mapping of an ENUM to a string.  In one instance, that string is the name of the hand and in another instance, it is a string (CSV) representation of of the digits in the hand. An added benefit is that the digits re returned in the order they would be for a proper poker hand.  For instance the hand 1,2,5,3,1 would be returned as ONE_PAIR (1,1,5,3,2). [Getting to the point] 1: using System; 2: using System.Collections.Generic; 3:   4: namespace DicePoker 5: { 6: using KVP_E2S = KeyValuePair<CDicePoker.E_DICE_POKER_HAND_VAL, string>; 7: public partial class CDicePoker 8: { 9: /// <summary> 10: /// Magical construction to determine the winner of given hand Key/Value. 11: /// </summary> 12: private static Dictionary<Predicate<int>, Func<List<KVP_E2S>, string>> 13: map_prd2fn = new Dictionary<Predicate<int>, Func<List<KVP_E2S>, string>> 14: { 15: {new Predicate<int>(i => i.Equals(0)), PlayerTie},//first tie 16:   17: {new Predicate<int>(i => i > 0), 18: (m => string.Format("Player One wins\n1={0}({1})\n2={2}({3})", 19: m[0].Key, m[0].Value, m[1].Key, m[1].Value))}, 20:   21: {new Predicate<int>(i => i < 0), 22: (m => string.Format("Player Two wins\n2={2}({3})\n1={0}({1})", 23: m[0].Key, m[0].Value, m[1].Key, m[1].Value))}, 24:   25: {new Predicate<int>(i => i.Equals(0)), 26: (m => string.Format("Tie({0}) \n1={1}\n2={2}", 27: m[0].Key, m[0].Value, m[1].Value))} 28: }; 29: } 30: } When this is called, the code calls the Invoke method of the predicate to return a bool.  The first on matching true will have its value invoked. 1: private static Func<DICE_HAND, E_DICE_POKER_HAND_VAL> GetHandEval = dh => 2: map_dph2fn[map_dph2fn.Keys.Where(enm2fn => enm2fn(dh)).First()]; After coming up with this process, I realized (with a little modification) it could be called to evaluate the individual values in the dice hand in the event of a tie. 1: private static Func<List<KVP_E2S>, string> PlayerTie = lst_kvp => 2: map_prd2fn.Skip(1) 3: .Where(x => x.Key.Invoke(RenderDigits(dhPlayerOne).CompareTo(RenderDigits(dhPlayerTwo)))) 4: .Select(s => s.Value) 5: .First().Invoke(lst_kvp); After that, I realized I could now create a program completely without “if” statements or “for” loops! 1: static void Main(string[] args) 2: { 3: Dictionary<Predicate<int>, Action<Action<string>>> main = new Dictionary<Predicate<int>, Action<Action<string>>> 4: { 5: {(i => i.Equals(0)), PlayGame}, 6: {(i => true), Usage} 7: }; 8:   9: main[main.Keys.Where(m => m.Invoke(args.Length)).First()].Invoke(Display); 10: } …and there you have it. :) ZIPPED Project

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• Goto for the Java Programming Language

  - by darcy

  Work on JDK 8 is well-underway, but we thought this late-breaking JEP for another language change for the platform couldn't wait another day before being published. Title: Goto for the Java Programming Language Author: Joseph D. Darcy Organization: Oracle. Created: 2012/04/01 Type: Feature State: Funded Exposure: Open Component: core/lang Scope: SE JSR: 901 MR Discussion: compiler dash dev at openjdk dot java dot net Start: 2012/Q2 Effort: XS Duration: S Template: 1.0 Reviewed-by: Duke Endorsed-by: Edsger Dijkstra Funded-by: Blue Sun Corporation Summary Provide the benefits of the time-testing goto control structure to Java programs. The Java language has a history of adding new control structures over time, the assert statement in 1.4, the enhanced for-loop in 1.5,and try-with-resources in 7. Having support for goto is long-overdue and simple to implement since the JVM already has goto instructions. Success Metrics The goto statement will allow inefficient and verbose recursive algorithms and explicit loops to be replaced with more compact code. The effort will be a success if at least twenty five percent of the JDK's explicit loops are replaced with goto's. Coordination with IDE vendors is expected to help facilitate this goal. Motivation The goto construct offers numerous benefits to the Java platform, from increased expressiveness, to more compact code, to providing new programming paradigms to appeal to a broader demographic. In JDK 8, there is a renewed focus on using the Java platform on embedded devices with more modest resources than desktop or server environments. In such contexts, static and dynamic memory footprint is a concern. One significant component of footprint is the code attribute of class files and certain classes of important algorithms can be expressed more compactly using goto than using other constructs, saving footprint. For example, to implement state machines recursively, some parties have asked for the JVM to support tail calls, that is, to perform a complex transformation with security implications to turn a method call into a goto. Such complicated machinery should not be assumed for an embedded context. A better solution is just to expose to the programmer the desired functionality, goto. The web has familiarized users with a model of traversing links among different HTML pages in a free-form fashion with some state being maintained on the side, such as login credentials, to effect behavior. This is exactly the programming model of goto and code. While in the past this has been derided as leading to "spaghetti code," spaghetti is a tasty and nutritious meal for programmers, unlike quiche. The invokedynamic instruction added by JSR 292 exposes the JVM's linkage operation to programmers. This is a low-level operation that can be leveraged by sophisticated programmers. Likewise, goto is a also a low-level operation that should not be hidden from programmers who can use more efficient idioms. Some may object that goto was consciously excluded from the original design of Java as one of the removed feature from C and C++. However, the designers of the Java programming languages have revisited these removals before. The enum construct was also left out only to be added in JDK 5 and multiple inheritance was left out, only to be added back by the virtual extension method methods of Project Lambda. As a living language, the needs of the growing Java community today should be used to judge what features are needed in the platform tomorrow; the language should not be forever bound by the decisions of the past. Description From its initial version, the JVM has had two instructions for unconditional transfer of control within a method, goto (0xa7) and goto_w (0xc8). The goto_w instruction is used for larger jumps. All versions of the Java language have supported labeled statements; however, only the break and continue statements were able to specify a particular label as a target with the onerous restriction that the label must be lexically enclosing. The grammar addition for the goto statement is: GotoStatement: goto Identifier ; The new goto statement similar to break except that the target label can be anywhere inside the method and the identifier is mandatory. The compiler simply translates the goto statement into one of the JVM goto instructions targeting the right offset in the method. Therefore, adding the goto statement to the platform is only a small effort since existing compiler and JVM functionality is reused. Other language changes to support goto include obvious updates to definite assignment analysis, reachability analysis, and exception analysis. Possible future extensions include a computed goto as found in gcc, which would replace the identifier in the goto statement with an expression having the type of a label. Testing Since goto will be implemented using largely existing facilities, only light levels of testing are needed. Impact Compatibility: Since goto is already a keyword, there are no source compatibility implications. Performance/scalability: Performance will improve with more compact code. JVMs already need to handle irreducible flow graphs since goto is a VM instruction.

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• The JavaOne 2012 Sunday Technical Keynote

  - by Janice J. Heiss

  At the JavaOne 2012 Sunday Technical Keynote, held at the Masonic Auditorium, Mark Reinhold, Chief Architect, Java Platform Group, stated that they were going to do things a bit differently--"rather than 20 minutes of SE, and 20 minutes of FX, and 20 minutes of EE, we're going to mix it up a little," he said. "For much of it, we're going to be showing a single application, to show off some of the great work that's been done in the last year, and how Java can scale well--from the cloud all the way down to some very small embedded devices, and how JavaFX scales right along with it."Richard Bair and Jasper Potts from the JavaFX team demonstrated a JavaOne schedule builder application with impressive navigation, animation, pop-overs, and transitions. They noted that the application runs seamlessly on either Windows or Macs, running Java 7. They then ran the same application on an Ubuntu Linux machine--"it just works," said Blair.The JavaFX duo next put the recently released JavaFX Scene Builder through its paces -- dragging and dropping various image assets to build the application's UI, then fine tuning a CSS file for the finished look and feel. Among many other new features, in the past six months, JavaFX has released support for H.264 and HTTP live streaming, "so you can get all the real media playing inside your JavaFX application," said Bair. And in their developer preview builds of JavaFX 8, they've now split the rendering thread from the UI thread, to better take advantage of multi-core architectures.Next, Brian Goetz, Java Language Architect, explored language and library features planned for Java SE 8, including Lambda expressions and better parallel libraries. These feature changes both simplify code and free-up libraries to more effectively use parallelism. "It's currently still a lot of work to convert an application from serial to parallel," noted Goetz.Reinhold had previously boasted of Java scaling down to "small embedded devices," so Blair and Potts next ran their schedule builder application on a small embedded PandaBoard system with an OMAP4 chip set. Connected to a touch screen, the embedded board ran the same JavaFX application previously seen on the desktop systems, but now running on Java SE Embedded. (The systems can be seen and tried at four of the nearby JavaOne hotels.) Bob Vandette, Java Embedded Architect, then displayed a $25 Rasberry Pi ARM-based system running Java SE Embedded, noting the even greater need for the platform independence of Java in such highly varied embedded processor spaces. Reinhold and Vandetta discussed Project Jigsaw, the planned modularization of the Java SE platform, and its deferral from the Java 8 release to Java 9. Reinhold demonstrated the promise of Jigsaw by running a modularized demo version of the earlier schedule builder application on the resource constrained Rasberry Pi system--although the demo gods were not smiling down, and the application ultimately crashed.Reinhold urged developers to become involved in the Java 8 development process--getting the weekly builds, trying out their current code, and trying out the new features:http://openjdk.java.net/projects/jdk8http://openjdk.java.net/projects/jdk8/spechttp://jdk8.java.netFrom there, Arun Gupta explored Java EE. The primary themes of Java EE 7, Gupta stated, will be greater productivity, and HTML 5 functionality (WebSocket, JSON, and HTML 5 forms). Part of the planned productivity increase of the release will come from a reduction in writing boilerplate code--through the widespread use of dependency injection in the platform, along with default data sources and default connection factories. Gupta noted the inclusion of JAX-RS in the web profile, the changes and improvements found in JMS 2.0, as well as enhancements to Java EE 7 in terms of JPA 2.1 and EJB 3.2. GlassFish 4 is the reference implementation of Java EE 7, and currently includes WebSocket, JSON, JAX-RS 2.0, JMS 2.0, and more. The final release is targeted for Q2, 2013. Looking forward to Java EE 8, Gupta explored how the platform will provide multi-tenancy for applications, modularity based on Jigsaw, and cloud architecture. Meanwhile, Project Avatar is the group's incubator project for designing an end-to-end framework for building HTML 5 applications. Santiago Pericas-Geertsen joined Gupta to demonstrate their "Angry Bids" auction/live-bid/chat application using many of the enhancements of Java EE 7, along with an Avatar HTML 5 infrastructure, and running on the GlassFish reference implementation.Finally, Gupta covered Project Easel, an advanced tooling capability in NetBeans for HTML5. John Ceccarelli, NetBeans Engineering Director, joined Gupta to demonstrate creating an HTML 5 project from within NetBeans--formatting the project for both desktop and smartphone implementations. Ceccarelli noted that NetBeans 7.3 beta will be released later this week, and will include support for creating such HTML 5 project types. Gupta directed conference attendees to: http://glassfish.org/javaone2012 for everything about Java EE and GlassFish at JavaOne 2012.

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• JavaOne Latin America Opening Keynotes

  - by Tori Wieldt

  Originally published on blogs.oracle.com/javaone It was a great first day at JavaOne Brazil, which included the Java Strategy and Java Technical keynotes. Henrik Stahl, Senior Director, Product Management for Java opened the keynotes by saying that this is the third year for JavaOne Latin America. He explained, "You know what they say, the first time doesn't count, the second time is a habit and the third time it's a tradition!" He mentioned that he was thrilled that this is largest JavaOne in Brazil to date, and he wants next year to be larger. He said that Oracle knows Latin America is an important hub for development.  "We continually come back to Latin America because of the dedication the community has with driving the continued innovation for Java," he said. Stahl explained that Oracle and the Java community must continue to innovate and Make the Future Java together. The success of Java depends on three important factors: technological innovation, Oracle as a strong steward of Java, and community participation. "The Latin American Java Community (especially in Brazil) is a shining example of how to be positive contributor to Java," Stahl said. Next, George Saab, VP software dev, Java Platform Group at Oracle, discussed some of the recent and upcoming changes to Java. "In addition to the incremental improvements to Java 7, we have also increased the set of platforms supported by Oracle from Linux, Windows, and Solaris to now also include Mac OS X and Linux/ARM for ARM-based PCs such as the Raspberry Pi and emerging ARM based microservers."  Saab announced that EA builds for Linux ARM Hard Float ABI will be available by the end of the year.  Staffan Friberg, Product Manager, Java Platform Group, provided an overview of some of the language coming in Java 8, including Lambda, remove of PermGen, improved data and time APIs and improved security, Java 8 development is moving along. He reminded the audience that they can go to OpenJDK to see this development being done in real-time, and that there are weekly early access builds of OracleJDK 8 that developers can download and try today. Judson Althoff, Senior Vice President, Worldwide Alliances and Channels and Embedded Sales, was invited to the stage, and the audience was told that "even though he is wearing a suit, he is still pretty technical." Althoff started off with a bang: "The Internet of Things is on a collision course with big data and this is a huge opportunity for developers."  For example, Althoff said, today cars are more a data device than a mechanical device. A car embedded with sensors for fuel efficiency, temperature, tire pressure, etc. can generate a petabyte of data A DAY. There are similar examples in healthcare (patient monitoring and privacy requirements creates a complex data problem) and transportation management (sending a package around the world with sensors for humidity, temperature and light). Althoff then brought on stage representatives from three companies that are successful with Java today, first Axel Hansmann, VP Strategy & Marketing Communications, Cinterion. Mr. Hansmann explained that Cinterion, a market leader in Latin America, enables M2M services with Java. At JavaOne San Francisco, Cinterion launched the EHS5, the smallest 3g solderable module, with Java installed on it. This provides Original Equipment Manufacturers (OEMs) with a cost effective, flexible platform for bringing advanced M2M technology to market.Next, Steve Nelson, Director of Marketing for the Americas, at Freescale explained that Freescale is #1 in Embedded Processors in Wired and Wireless Communications, and #1 in Automotive Semiconductors in the Americas. He said that Java provides a mature, proven platform that is uniquely suited to meet the requirements of almost any type of embedded device. He encouraged University students to get involved in the Freescale Cup, a global competition where student teams build, program, and race a model car around a track for speed.Roberto Franco, SBTVD Forum President, SBTVD, talked about Ginga, a Java-based standard for television in Brazil. He said there are 4 million Ginga TV sets in Brazil, and they expect over 20 million TV sets to be sold by the end of 2014. Ginga is also being adopted in other 11 countries in Latin America. Ginga brings interactive services not only at TV set, but also on other devices such as tablets,  PCs or smartphones, as the main or second screen. "Interactive services is already a reality," he said, ' but in a near future, we foresee interactivity enhanced TV content, convergence with OTT services and a big participation from the audience,  all integrated on TV, tablets, smartphones and second screen devices."Before he left the stage, Nandini Ramani thanked Judson for being part of the Java community and invited him to the next Geek Bike Ride in Brazil. She presented him an official geek bike ride jersey.For the Technical Keynote, a "blue screen of death" appeared. With mock concern, Stephin Chin asked the rest of the presenters if they could go on without slides. What followed was a interesting collection of demos, including JavaFX on a tablet, a look at Project Easel in NetBeans, and even Simon Ritter controlling legos with his brainwaves! Stay tuned for more dispatches.

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• JavaOne Latin America Opening Keynotes

  - by Tori Wieldt

  It was a great first day at JavaOne Brazil, which included the Java Strategy and Java Technical keynotes. Henrik Stahl, Senior Director, Product Management for Java opened the keynotes by saying that this is the third year for JavaOne Latin America. He explained, "You know what they say, the first time doesn't count, the second time is a habit and the third time it's a tradition!" He mentioned that he was thrilled that this is largest JavaOne in Brazil to date, and he wants next year to be larger. He said that Oracle knows Latin America is an important hub for development.  "We continually come back to Latin America because of the dedication the community has with driving the continued innovation for Java," he said. Stahl explained that Oracle and the Java community must continue to innovate and Make the Future Java together. The success of Java depends on three important factors: technological innovation, Oracle as a strong steward of Java, and community participation. "The Latin American Java Community (especially in Brazil) is a shining example of how to be positive contributor to Java," Stahl said. Next, George Saab, VP software dev, Java Platform Group at Oracle, discussed some of the recent and upcoming changes to Java. "In addition to the incremental improvements to Java 7, we have also increased the set of platforms supported by Oracle from Linux, Windows, and Solaris to now also include Mac OS X and Linux/ARM for ARM-based PCs such as the Raspberry Pi and emerging ARM based microservers."  Saab announced that EA builds for Linux ARM Hard Float ABI will be available by the end of the year.  Staffan Friberg, Product Manager, Java Platform Group, provided an overview of some of the language coming in Java 8, including Lambda, remove of PermGen, improved data and time APIs and improved security, Java 8 development is moving along. He reminded the audience that they can go to OpenJDK to see this development being done in real-time, and that there are weekly early access builds of OracleJDK 8 that developers can download and try today. Judson Althoff, Senior Vice President, Worldwide Alliances and Channels and Embedded Sales, was invited to the stage, and the audience was told that "even though he is wearing a suit, he is still pretty technical." Althoff started off with a bang: "The Internet of Things is on a collision course with big data and this is a huge opportunity for developers."  For example, Althoff said, today cars are more a data device than a mechanical device. A car embedded with sensors for fuel efficiency, temperature, tire pressure, etc. can generate a petabyte of data A DAY. There are similar examples in healthcare (patient monitoring and privacy requirements creates a complex data problem) and transportation management (sending a package around the world with sensors for humidity, temperature and light). Althoff then brought on stage representatives from three companies that are successful with Java today, first Axel Hansmann, VP Strategy & Marketing Communications, Cinterion. Mr. Hansmann explained that Cinterion, a market leader in Latin America, enables M2M services with Java. At JavaOne San Francisco, Cinterion launched the EHS5, the smallest 3g solderable module, with Java installed on it. This provides Original Equipment Manufacturers (OEMs) with a cost effective, flexible platform for bringing advanced M2M technology to market.Next, Steve Nelson, Director of Marketing for the Americas, at Freescale explained that Freescale is #1 in Embedded Processors in Wired and Wireless Communications, and #1 in Automotive Semiconductors in the Americas. He said that Java provides a mature, proven platform that is uniquely suited to meet the requirements of almost any type of embedded device. He encouraged University students to get involved in the Freescale Cup, a global competition where student teams build, program, and race a model car around a track for speed.Roberto Franco, SBTVD Forum President, SBTVD, talked about Ginga, a Java-based standard for television in Brazil. He said there are 4 million Ginga TV sets in Brazil, and they expect over 20 million TV sets to be sold by the end of 2014. Ginga is also being adopted in other 11 countries in Latin America. Ginga brings interactive services not only at TV set, but also on other devices such as tablets,  PCs or smartphones, as the main or second screen. "Interactive services is already a reality," he said, ' but in a near future, we foresee interactivity enhanced TV content, convergence with OTT services and a big participation from the audience,  all integrated on TV, tablets, smartphones and second screen devices."Before he left the stage, Nandini Ramani thanked Judson for being part of the Java community and invited him to the next Geek Bike Ride in Brazil. She presented him an official geek bike ride jersey.For the Technical Keynote, a "blue screen of death" appeared. With mock concern, Stephin Chin asked the rest of the presenters if they could go on without slides. What followed was a interesting collection of demos, including JavaFX on a tablet, a look at Project Easel in NetBeans, and even Simon Ritter controlling legos with his brainwaves! Stay tuned for more dispatches.

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• JavaOne 2012 Sunday Strategy Keynote

  - by Janice J. Heiss

  At the Sunday Strategy Keynote, held at the Masonic Auditorium, Hasan Rizvi, EVP, Middleware and Java Development, stated that the theme for this year's JavaOne is: “Make the future Java”-- meaning that Java continues in its role as the most popular, complete, productive, secure, and innovative development platform. But it also means, he qualified, the process by which we make the future Java -- an open, transparent, collaborative, and community-driven evolution. "Many of you have bet your businesses and your careers on Java, and we have bet our business on Java," he said.Rizvi detailed the three factors they consider critical to the success of Java--technology innovation, community participation, and Oracle's leadership/stewardship. He offered a scorecard in these three realms over the past year--with OS X and Linux ARM support on Java SE, open sourcing of JavaFX by the end of the year, the release of Java Embedded Suite 7.0 middleware platform, and multiple releases on the Java EE side. The JCP process continues, with new JSR activity, and JUGs show a 25% increase in participation since last year. Oracle, meanwhile, continues its commitment to both technology and community development/outreach--with four regional JavaOne conferences last year in various part of the world, as well as the release of Java Magazine, with over 120,000 current subscribers. Georges Saab, VP Development, Java SE, next reviewed features of Java SE 7--the first major revision to the platform under Oracle's stewardship, which has included near-monthly update releases offering hundreds of fixes, performance enhancements, and new features. Saab indicated that developers, ISVs, and hosting providers have all been rapid adopters of the platform. He also noted that Oracle's entire Fusion middleware stack is supported on SE 7. The supported platforms for SE 7 has also increased--from Windows, Linux, and Solaris, to OS X, Linux ARM, and the emerging ARM micro-server market. "In the last year, we've added as many new platforms for Java, as were added in the previous decade," said Saab.Saab also explored the upcoming JDK 8 release--including Project Lambda, Project Nashorn (a modern implementation of JavaScript running on the JVM), and others. He noted that Nashorn functionality had already been used internally in NetBeans 7.3, and announced that they were planning to contribute the implementation to OpenJDK. Nandini Ramani, VP Development, Java Client, ME and Card, discussed the latest news pertaining to JavaFX 2.0--releases on Windows, OS X, and Linux, release of the FX Scene Builder tool, the JavaFX WebView component in NetBeans 7.3, and an OpenJFX project in OpenJDK. Nandini announced, as of Sunday, the availability for download of JavaFX on Linux ARM (developer preview), as well as Scene Builder on Linux. She noted that for next year's JDK 8 release, JavaFX will offer 3D, as well as third-party component integration. Avinder Brar, Senior Software Engineer, Navis, and Dierk König, Canoo Fellow, next took the stage and demonstrated all that JavaFX offers, with a feature-rich, animation-rich, real-time cargo management application that employs Canoo's just open-sourced Dolphin technology.Saab also explored Java SE 9 and beyond--Jigsaw modularity, Penrose Project for interoperability with OSGi, improved multi-tenancy for Java in the cloud, and Project Sumatra. Phil Rogers, HSA Foundation President and AMD Corporate Fellow, explored heterogeneous computing platforms that combine the CPU and the parallel processor of the GPU into a single piece of silicon and shared memory—a hardware technology driven by such advanced functionalities as HD video, face recognition, and cloud workloads. Project Sumatra is an OpenJDK project targeted at bringing Java to such heterogeneous platforms--with hardware and software experts working together to modify the JVM for these advanced applications and platforms.Ramani next discussed the latest with Java in the embedded space--"the Internet of things" and M2M--declaring this to be "the next IT revolution," with Java as the ideal technology for the ecosystem. Last week, Oracle released Java ME Embedded 3.2 (for micro-contollers and low-power devices), and Java Embedded Suite 7.0 (a middleware stack based on Java SE 7). Axel Hansmann, VP Strategy and Marketing, Cinterion, explored his company's use of Java in M2M, and their new release of EHS5, the world's smallest 3G-capable M2M module, running Java ME Embedded. Hansmaan explained that Java offers them the ability to create a "simple to use, scalable, coherent, end-to-end layer" for such diverse edge devices.Marc Brule, Chief Financial Office, Royal Canadian Mint, also explored the fascinating use-case of JavaCard in his country's MintChip e-cash technology--deployable on smartphones, USB device, computer, tablet, or cloud. In parting, Ramani encouraged developers to download the latest releases of Java Embedded, and try them out.Cameron Purdy, VP, Fusion Middleware Development and Java EE, summarized the latest developments and announcements in the Enterprise space--greater developer productivity in Java EE6 (with more on the way in EE 7), portability between platforms, vendors, and even cloud-to-cloud portability. The earliest version of the Java EE 7 SDK is now available for download--in GlassFish 4--with WebSocket support, better JSON support, and more. The final release is scheduled for April of 2013. Nicole Otto, Senior Director, Consumer Digital Technology, Nike, explored her company's Java technology driven enterprise ecosystem for all things sports, including the NikeFuel accelerometer wrist band. Looking beyond Java EE 7, Purdy mentioned NoSQL database functionality for EE 8, the concurrency utilities (possibly in EE 7), some of the Avatar projects in EE 7, some in EE 8, multi-tenancy for the cloud, supporting SaaS applications, and more.Rizvi ended by introducing Dr. Robert Ballard, oceanographer and National Geographic Explorer in Residence--part of Oracle's philanthropic relationship with the National Geographic Society to fund K-12 education around ocean science and conservation. Ballard is best known for having discovered the wreckage of the Titanic. He offered a fascinating video and overview of the cutting edge technology used in such deep-sea explorations, noting that in his early days, high-bandwidth exploration meant that you’d go down in a submarine and "stick your face up against the window." Now, it's a remotely operated, technology telepresence--"I think of my Hercules vehicle as my equivalent of a Na'vi. When I go beneath the sea, I actually send my spirit." Using high bandwidth satellite links, such amazing explorations can now occur via smartphone, laptop, or whatever platform. Ballard’s team regularly offers live feeds and programming out to schools and the world, spanning 188 countries--with embedding educators as part of the expeditions. It's technology at its finest, inspiring the next-generation of scientists and explorers!

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• concurrency::index<N> from amp.h

  - by Daniel Moth

  Overview C++ AMP introduces a new template class index<N>, where N can be any value greater than zero, that represents a unique point in N-dimensional space, e.g. if N=2 then an index<2> object represents a point in 2-dimensional space. This class is essentially a coordinate vector of N integers representing a position in space relative to the origin of that space. It is ordered from most-significant to least-significant (so, if the 2-dimensional space is rows and columns, the first component represents the rows). The underlying type is a signed 32-bit integer, and component values can be negative. The rank field returns N. Creating an index The default parameterless constructor returns an index with each dimension set to zero, e.g. index<3> idx; //represents point (0,0,0) An index can also be created from another index through the copy constructor or assignment, e.g. index<3> idx2(idx); //or index<3> idx2 = idx; To create an index representing something other than 0, you call its constructor as per the following 4-dimensional example: int temp[4] = {2,4,-2,0}; index<4> idx(temp); Note that there are convenience constructors (that don’t require an array argument) for creating index objects of rank 1, 2, and 3, since those are the most common dimensions used, e.g. index<1> idx(3); index<2> idx(3, 6); index<3> idx(3, 6, 12); Accessing the component values You can access each component using the familiar subscript operator, e.g. One-dimensional example: index<1> idx(4); int i = idx[0]; // i=4 Two-dimensional example: index<2> idx(4,5); int i = idx[0]; // i=4 int j = idx[1]; // j=5 Three-dimensional example: index<3> idx(4,5,6); int i = idx[0]; // i=4 int j = idx[1]; // j=5 int k = idx[2]; // k=6 Basic operations Once you have your multi-dimensional point represented in the index, you can now treat it as a single entity, including performing common operations between it and an integer (through operator overloading): -- (pre- and post- decrement), ++ (pre- and post- increment), %=, *=, /=, +=, -=,%, *, /, +, -. There are also operator overloads for operations between index objects, i.e. ==, !=, +=, -=, +, –. Here is an example (where no assertions are broken): index<2> idx_a; index<2> idx_b(0, 0); index<2> idx_c(6, 9); _ASSERT(idx_a.rank == 2); _ASSERT(idx_a == idx_b); _ASSERT(idx_a != idx_c); idx_a += 5; idx_a[1] += 3; idx_a++; _ASSERT(idx_a != idx_b); _ASSERT(idx_a == idx_c); idx_b = idx_b + 10; idx_b -= index<2>(4, 1); _ASSERT(idx_a == idx_b); Usage You'll most commonly use index<N> objects to index into data types that we'll cover in future posts (namely array and array_view). Also when we look at the new parallel_for_each function we'll see that an index<N> object is the single parameter to the lambda, representing the (multi-dimensional) thread index… In the next post we'll go beyond being able to represent an N-dimensional point in space, and we'll see how to define the N-dimensional space itself through the extent<N> class. Comments about this post by Daniel Moth welcome at the original blog.

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