mixin template bug with opBinary?

[Steven Schveighoffer]

On 7/22/22 8:33 AM, Anthony Quizon wrote:
> Hello,
> 
> I'm trying to create a mixin for quick binary operator overloads by 
> passing in types with a corresponding associative array of strings to 
> functions. However,
> the code I currently have:
> 
> ```
> module foo;
> 
> mixin template opBi(
>      A, A function(A, A)[string] f0,
> ) {
>      static foreach (k, f; f0) { A opBinary(string op: k)(A r) { return 
> f(this, r); } }
> }
> 
> struct A {
>      mixin opBi!(
>          A, [ "+": (A a, A b) => a],
>      );
> }
> 
> struct B {
>      mixin opBi!(
>          B, [ "+": (B a, B b) => a],
>      );
> }
> 
> 
> ```
> 
> Will not let me override operators on both struct A and B.
> 
> I get:
> ```
> foo.d(16): Error: mixin `foo.B.opBi!(B, ["+":function (B a, B b) pure 
> nothrow @nogc @safe => a])` does not match template declaration `opBi(A, 
> A function(A, A)[string] f0)`
> ```
> 
> Is this a bug or am I doing something wrong?

It's typing the AA differently, and therefore it doesn't fit. The type 
of the AA you are passing in is `T1[string]`, where it's expecting 
`T2[string]`, where:

`T1` is `B function(B, B) pure nothrow @nogc @safe`
`T2` is `B function(B, B)`

I don't know if there's a better way to do this, other than use a 
further template parameter to match the function type passed in.

-Steve