Re: Closures and loop scope

[Andrei Alexandrescu]

On 6/4/13 5:03 PM, Nick Sabalausky wrote:
On Tue, 04 Jun 2013 21:19:56 +0200
"Idan Arye"<generic...@gmail.com>  wrote:
Consider the following code. What will it print?

      auto arr=new ulong delegate()[5];

      foreach(i;0..arr.length){
          arr[i]=()=>i;
      }

      writeln(arr.map!`a()`());

It is natural to expect that it will print [0, 1, 2, 3, 4], but
it actually prints [5, 5, 5, 5, 5]. The reason is obvious - all
the delegates refer to the same `i` in their closures, and at the
end of the loop that `i` is set to `5`.


I think the problem is simply a misunderstanding of closures.

FWIW this was discussed at a C# conference. It was a change of behavior 
or something. It was a sort of a big deal, and a matter in which 
reasonable people were disagreeing.

Andrei