Templated function (free nor member) cannot return by-ref explicitly (i.e. not with auto ref) if instantiation arguments are infered and the instantiation arguments contain at least one value argument.


This does not compile:
--------------------
void main()
{
    S s;
    s.opDispatch!"bar"(42); // fails
}
struct S
{
    ref int opDispatch(string str, T)(T arg)
    {
        return _xyz;
    }
    int _xyz;
}
--------------------
% dmd -o- -c test
test.d(8): Error: variable test.S.str only parameters or foreach declarations can be ref
--------------------


The error does not occur if the template instantiation arguments are not infered:
--------------------
void main()
{
    S s;
    s.opDispatch!("bar", int)(42); // fine
}
...
--------------------


Auto ref is fine:
--------------------
void main()
{
    S s;
    s.opDispatch!"bar"(42); // fine
}
struct S
{
    auto ref opDispatch(string str, T)(T arg)
    {
        return _xyz;
    }
    int _xyz;
}
--------------------


This is a workaround for opDispatch:
--------------------
struct S
{
    template opDispatch(string str)
    {
        ref int opDispatch(T)(T arg)
        {
            return _xyz;
        }
    }
    int _xyz;
}
--------------------