Ultra-pure map()?

[John Colvin]

On Saturday, 28 December 2013 at 01:41:35 UTC, David Held wrote:
> import std.algorithm;
> import std.stdio;
> import std.conv;
>
> class Trivial
> {
>     int sideEffect() { return n++; }
>     override string toString() pure { return to!string(n); }
>     int n;
> }
>
> void main()
> {
>     Trivial[] objs = [ new Trivial ];
>     map!(o => o.sideEffect())(objs);
>     writeln(objs);	// [0]
>     foreach (o; objs) o.sideEffect();
>     writeln(objs);	// [1]
> }
>
> Can someone explain to me why map() is not equivalent to 
> foreach in the code above?  From what I can tell, map() doesn't 
> do anything at all on objs, even though it is a perfectly 
> legitimate range (as far as I can tell).
>
> Dave

Map is lazy and is never iterated over in your code, therefore no 
side effects.