On Sunday, 1 May 2022 at 03:57:12 UTC, Elfstone wrote:
module test;
struct MatrixImpl(S, size_t M, size_t N)
{
}
template Vector(S, size_t N)
{
alias Vector = MatrixImpl!(S, 1, N);
}
@nogc
S dot1(S, size_t N)(in Vector!(S, N) lhs, in Vector!(S, N)
rhs)
{
return 0;
}
@nogc
S dot2(S, size_t N)(in MatrixImpl!(S, 1, N) lhs, in
MatrixImpl!(S, 1, N) rhs)
{
return 0;
}
unittest
{
import std.stdio;
Vector!(float, 2) a, b;
dot1(a, b); // Error: none of the overloads of template
`test.dot1` are callable using argument types
`!()(MatrixImpl!(float, 1LU, 2LU), MatrixImpl!(float, 1LU,
2LU))`
// Candidate is: `dot1(S, ulong N)(in
Vector!(S, N) lhs, in Vector!(S, N) rhs)`
dot2(a, b); // compiles
static if (is(Vector!(float, 2) == MatrixImpl!(float,
1, 2)))
{
writeln("WTH"); // prints
}
}
It's natural to declare it the way dot1 is declared, isn't it?
Is this a bug?
Or I simply can't assume alias works the way I thought it would.
Can I work around it, without falling back to the abominable
dot2?
Template deduction for aliased function parameter is a very
tricky argument and it's not so simple to handle in certain
cases. Consider for example this code:
```d
template MyAlias(T){
alias MyAlias = int;
}
T simp(T)(MyAlias!T val){
return T.init;
}
int main(){
simp(3);//Impossible to deduce T
simp( cast(MyAlias!string) 4);//Also invalid since
MyAlias!string is exactly int
simp!string(4);//Ok, no parameter deduction
}
```
Instead to use aliases it's better (both in D and in C++) to use
constraints/concepts.
