Closure capture loop variables

[Vladimir Panteleev via Digitalmars-d]

On Thursday, 30 April 2015 at 01:16:20 UTC, Freddy wrote:
> I understand that
> ----
> import std.stdio;
> void main(){
> 	int delegate() func;
> 	foreach(i;0..10){
> 		if(i==5){
> 			func= () => i;
> 		}
> 	}
> 	writeln(func());//9
> }
> ----
> captures the loop variable,but why does
> ----
> import std.stdio;
>
> void main(){
> 	int delegate() func;
> 	foreach(i;0..10){
> 		auto copy=i;
> 		if(i==5){
> 			func= () => copy;
> 		}
> 	}
> 	writeln(func());//should be 5
> }
>
> ----
> still print 9.

Because "copy" is still modified every time "i" is.

You can either put "copy" inside the "if":

----
import std.stdio;

void main(){
	int delegate() func;
	foreach(i;0..10){
		if(i==5){
			auto copy=i;
			func= () => copy;
		}
	}
	writeln(func());//should be 5
}
----

Or you can create a closure for each iteration:

----
import std.stdio;

void main(){
	int delegate() func;
	foreach(i;0..10){
		(){
			auto copy=i;
			if(i==5){
				func= () => copy;
			}
		}();
	}
	writeln(func());//should be 5
}
----