Re: 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
}
----