What are 'closures' in .NET?

In essence, a closure is a block of code that can be executed at a later time, but which maintains the environment in which it was first created - i.e. it can still use the local variables, etc of the method which created it, even after that method has finished executing.

The general feature of closures is implemented in C# by anonymous methods and lambda expressions.

Here's an example using an anonymous method:

using System;

class Test
{
   static void Main()
   {
       Action action = CreateAction();
       action();
       action();
   }

   static Action CreateAction()
   {
       int counter = 0;
       return delegate
       {
           // Yes, it could be done in one statement;
           // but it is clearer like this.
           counter++;
           Console.WriteLine("counter={0}", counter);
       };
   }
}

Output:
counter=1
counter=2

Here we can see that the action returned by CreateAction still has access to the counter variable, and can indeed increment it, even though CreateAction itself has finished.

Comments

gcAllowVeryLargeObjects Element

There are numerous new features coming with .NET 4.5 and here, on this blog, you can find several posts about it. But the feature we are goint to talk about today is very exciting, because we were waiting for it more than 10 years. Since .NET 1.0 the memory limit of .NET object is 2GB. This means you cannot for example create array which contains elements with more than 2GB in total. If try to create such array, you will get the OutOfMemoryException. Let’s see an example how to produce OutOfMemoryException. Before that Open Visual Studio 2012, and create C# Console Application, like picture below. First lets create simple struct with two double members like example below: 1 2 3 4 5 6 7 8 9 10 11 12 public struct ComplexNumber { public double Re; public double Im; public ComplexNumber( double re, double im) { Re=re; Im=im; } } As we know this structure consumes about 16

Support for debugging lambda expressions with Visual Studio 2015

Anyone who uses LINQ (or lambdas in general) and the debugger will quickly discover the dreaded message “Expression cannot contain lambda expressions”. Lack of lambda support has been a limitation of the Visual Studio Debugger ever since Lambdas were added to C# and Visual Basic. With visual studio 2015 Microsoft has added support for debugging lambda expressions. Let’s first look at an example, and then I’ll walk you through current limitations. Example To try this yourself, create a new C# Console app with this code: using System.Diagnostics; using System.Linq; class Program { static void Main() { float[] values = Enumerable.Range(0, 100).Select(i => (float)i / 10).ToArray(); Debugger.Break(); } } Then compile, start debugging, and add “values.Where(v => (int)v == 3).ToArray()” in the Watch window. You’ll be happy to see the same as what the screenshot above shows you. I am using Visual Studio 2015 Preview and it has some limitations.

How to allow a very large object in .net application?

Since .NET 1.0 the memory limit of .NET object is 2GB. This means you cannot for example create array which contains elements with more than 2GB in total. If try to create such array, you will get the OutOfMemoryException. Let’s see an example how to produce OutOfMemoryException. Before that Open Visual Studio, and create C# Console Application. Lets create simple struct with two double members like example below: public struct ComplexNumber { public double Re; public double Im; public ComplexNumber(double re, double im) { Re = re; Im = im; } } As we know this structure consumes about 16 bytes of memory. So if we want to create array of this type which consume more than 2GB we need to create array at least with 134217728 instances. So this sample program below creates 130000000 (about 1,97 GB) of array. int maxCount = 130000000; ComplexNumber[] arr = null; try { arr = new ComplexNumber[maxCount]; } catch (Exception ex) { Console.WriteLine(ex.Message); } So if we run t

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