Modifing local variables with anonymous delegate?

[Gordon]

On Thursday, 26 December 2013 at 23:52:09 UTC, Adam D. Ruppe 
wrote:
> On Thursday, 26 December 2013 at 23:23:02 UTC, Gordon wrote:
>> But the "b" in "main" retains its original value of 42.
>
> Try printing the b in main again AFTER printing c. You should 
> see the change.
>
> std.algorithm for the most part doesn't actually do any of its 
> calculations until it has to. This allows it to save speed 
> skipping work it doesn't need, and make it possible to map 
> infinite series and stuff like that.
>
> So the line c = map....; just prepares the calculation, it 
> doesn't actually run the function. The writeln(c) forces 
> evaluation. You can also force evaluation immediately by 
> calling .array on the thing, which calculates it and puts the 
> result in a new array.

Thanks!