On 31.12.2015 23:37, rcorre wrote:
struct Vector(T, int N) { }
alias Vector2(T) = Vector!(T, 2);
void fun1(T)(Vector!(T, 2) vec) { }
void fun2(T)(Vector2!T vec) { }
unittest {
fun1(Vector!(float, 2).init);
fun2(Vector!(float, 2).init);
}
Why can fun1 deduce `T`, but fun2 can't?
Failure:
"template d.fun2 cannot deduce function from argument types
!()(Vector!(float, 2))"?
Vector2 is a little more than just an alias, it's a template for aliases.
Your Vector2 is short for this:
----
template Vector2(T)
{
alias Vector2 = Vector!(T, 2);
}
----
You can see that such a template could map different T types to the same
result type. For example, Vector2!int and Vector2!long could both become
aliases to Vector!(long, 2). Deducing T from a Vector!(long, 2) argument
would be ambiguous then. T could be int or long, and there is no way to
tell what it should be.
That's just how I make sense of this, though. I'm not sure if it's the
whole picture.
