Proposal: delegates as aggregates in foreach statements

[Bruno Medeiros]

Chris Nicholson-Sauls wrote:
> An idea occurred to me last night, which I'm sure must have come up 
> before.  If it hasn't, I'm shocked, but I'm bringing it up (again?) 
> anyway.  Why not allow a delegate (or even function pointer?) to be used 
> as the "aggregate" parameter to a foreach statement, requiring that it 
> expose the same signature as a valid opApply method?  For example:
> 
> # class Foo {
> #   private int[] p_data;
> #
> #   int opApply (int delegate(inout size_t, inout int) dg) {
> #     int result = 0;
> #     foreach (inout i, inout x; p_data) {
> #       result = dg(i, x);
> #       if (result)
> #         break;
> #     }
> #     return result;
> #   }
> #
> #   int reverse (int delegate(inout size_t, inout int) dg) {
> #     int result = 0;
> #     foreach (inout i, inout x; p_data.reverse) {
> #       result = dg(i, x);
> #       if (result)
> #         break;
> #     }
> #     return result;
> #   }
> # }
> #
> # Foo foo = new Foo;
> # foreach (size_t i, int x; &foo.reverse)
> #   // ... do stuff ...
> 
> One could even get real cute and use anonymous delegates:
> 
> # foreach (size_t i, inout char[] x;
> #   delegate int(int delegate (inout size_t ii, inout char[] xx) {
> #     // implement iterator logic
> #   }
> # ) {
> #   // ... do stuff ...
> # }
> 
> This, I think, would stand in the place of many uses of iterator objects 
> and mutators.
> 
> -- Chris Nicholson-Sauls

Hum, seems like a sound proposal. I think it could be good.


-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D