Return type inference on template

[Timon Gehr]

On 07/10/2012 04:14 PM, Andrea Fontana wrote:
> Simple template:
>
> T test(T)() { return T.init; }
>
> This code give error:
>
> int myVar;
> myVar = test();
>
> Why? Can't compiler guess T == int?
>

Type deduction only proceeds in the direction the data flows.

Reversing this process would in principle work in a few cases, such as
the one you present here.

I think it would be neat to have more powerful IFTI. An even more
important improvement would be to allow parameters to cross-talk, eg:

auto map(R,S,T...)(R range, S delegate(ElementType!R) dg) { ... }

[1,2,3].map(x=>2*x); // currently an error, but could be made to work

Note that full type inference cannot be achieved in D, because the type
system is Turing complete.