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digitalmars.D.learn - Questions to template overload resolution

1) T foo(T:SomeClass)(T arg){..}
It is specified on the main page that this template will match against
instantiations with a subclass of SomeClass. Will this also duplicate the
code? Or will the template work similar to the function T foo(SomeClass
arg){..}? If yes, why should normal functions and function templates without
type params be separated at all?

2) Why is this an error? Obviously, the second template is a better match.

What is the rationale for requiring the clumsier f(T:double,U:int)(T a,U b) to
f()(double a,int b) to allow proper overload resolution?

import std.stdio;

T f(T,U)(T a,U b){
    return a;
T f()(double a,int b){
    return a;

void main(){
test.d(11): Error: template test.f(T,U) f(T,U) matches more than one template
declaration, test.d(3):f(T,U) and test.d(6):f()
Apr 12 2011