To lessen the function pointers/delegates distinction

[David]

Am 05.03.2013 03:36, schrieb bearophile:
> I am thinking about one enhancement request, but I am not sure if the
> idea is meaningful, so I show it here first.
> 
> The presence of both function pointers and delegates makes the usage of
> higher order functions harder in D compared to function languages.
> 
> So maybe it's possible to support this code in D:
> 
> int foo(int x) { return x; }
> void bar(int delegate(int) dg) {}
> void main() {
>     bar(&foo);
> }
> 
> 
> DMD 2.063alpha gives:
> 
> temp.d(4): Error: function temp.bar (int delegate(int) dg) is not
> callable using argument types (int function(int x))
> temp.d(4): Error: cannot implicitly convert expression (& foo) of type
> int function(int x) to int delegate(int)
> 
> 
> 
> If you don't like implicit casts, then a possible alternative syntax:
> 
> int foo(int x) { return x; }
> void bar(int delegate(int) dg) {}
> void main() {
>     bar(cast(delegate)&foo);
> }
> 
> - - - - - - - - - -
> 
> An usage example where the difference between function pointers and
> delegates makes things much harder than necessary:
> 
> 
> import std.stdio, std.algorithm;
> T delegate(S) compose(T, U, S)(immutable T delegate(U) f,
>                                immutable U delegate(S) g) {
>     return s => f(g(s));
> }
> void main() {
>     int delegate(int)[] functions = [x => x * 3,
>                                      x => x * x,
>                                      x => x + 2];
>     auto allFunctions = functions.reduce!compose;
>     allFunctions(5).writeln;
> }
> 
> 
> This works, but if you try to change that code a little, the compilation
> will fail in a surprisingly large variety of cases.
> 
> Bye,
> bearophile

http://dlang.org/phobos/std_functional.html#.toDelegate ?