Erroneous usage of variable capture in loops

[ketmar via Digitalmars-d]

FreeSlave wrote:

> As known this code will not work as we may expect:
>
> import std.stdio;
>
> void main(string[] args)
> {
>      void delegate ()[] delegates;
>      foreach(i; 0..10) {
>          int j = i;
>          delegates ~= delegate() {
>              writeln(j);
>          };
>      }
>      foreach(dlgt; delegates) {
>          dlgt();
>      }
> }
>
> All delegates will capture the last value of 'j'.
>
> dmd does not complain about such case at all. Once I made this mistake 
> myself but noticed it thanks to unittesting. Recently I found similar 
> erroneous code in dlangui (no PR yet). Probably there are more projects 
> that have the same mistake unnoticed.
>
> May be compiler should produce error or at least generate warning on this 
> code.

i'm not even sure that it is detectable. what if i'll insert:

	if (i == args.length) break;

i.e. i *know* about the effect, and still want to do it? i can use it to 
capture some struct and break, for example. detecting this is kind of 
halting problem. and there is absolutely no way to hush the compiler, so it 
will always emit warning.