Southern BITS of Technical Goodness

Summary:

When you define a closure within the context of a loop, the closure is defined with the final value of anything iterated over in the loop. If this sounds strange, that’s because it is. See the simple example below.

The Code:

Download: [C# File] [Zipped Console Project]

The curious part is the simple PrintMe delegate that takes no arguments & returns nothing.

delegate void PrintMe();

Within the foreach loop where we iterate over the int array {1,2,3,4}, we define a closure (delegate) that merely prints i the integer being iterated.

(PrintMe)delegate(){    Console.WriteLine(i);   }

The Output:

You might expect the output, when we invoke each PrintMe delegate to be 1, 2, 3 & 4, but instead the output is 4, 4, 4, 4.

Solution:

By copying the value of i to a local variable j and the expected result is the actual result. We iterate over the integer array { 1,2,3,4 } and we print { 1,2,3,4 }.

This one line is the strange fix.

int j = i;

Just use j in the closure instead of i

(PrintMe)delegate()
         {
             Console.WriteLine(j);
         }

Download: [C# File] [Zipped Console Project]

alan.huffman C#, Modified Closures .NET, C#, Closures, Functional Programming, Quirks