Picking function templates with __traits(getOverloads, ..., true)

Jean-Louis Leroy jl at leroy.nyc
Wed Jul 29 23:57:21 UTC 2020

This works:

module test;

void foo(T)(T a, T b) {}
void foo(T)(char a, T b) {}

template InstantiateTemplateAt(alias Module, string name, int 
index, T...) {
     alias Template = __traits(getOverloads, test, name, 
     alias InstantiateTemplateAt = Template!(T);

pragma(msg, typeof(InstantiateTemplateAt!(test, "foo", 1, int)));
// pure nothrow @nogc @safe void(char a, int b)

class Matrix(T) {}

Matrix!T times(T)(Matrix!T a, T b);
// Matrix!T times(T)(T a, Matrix!T b); // <-- second 'times' 

pragma(msg, typeof(InstantiateTemplateAt!(test, "times", 0, 
// Matrix!int(Matrix!int a, int b)

But if I uncomment the second 'times' function template, I get an 

templateoverloads.d(8): Error: template `test.times` matches more 
than one template declaration:
templateoverloads.d(16):     `times(T)(Matrix!T a, T b)`
templateoverloads.d(17):     `times(T)(T a, Matrix!T b)`
templateoverloads.d(19): Error: template instance 
`test.InstantiateTemplateAt!(test, "times", 0, int)` error 

I may be missing the obvious...or it's a compiler bug???
(not sure if this belongs to the Learn section either)

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