• Andrea Fontana (6/6) Jul 10 2012 Simple template:
• Timon Gehr (10/16) Jul 10 2012 Type deduction only proceeds in the direction the data flows.

Andrea Fontana <advmail katamail.com> writes:

Simple template:

T test(T)() { return T.init; }

This code give error:

int myVar;
myVar =3D test();

Why? Can't compiler guess T =3D=3D int?

Timon Gehr <timon.gehr gmx.ch> writes:

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.