Hi,

I'm trying to write a template function which takes a templated alias to another type:

struct test(T)
{
}

template aliasT(T)
{
    alias test!(T) aliasT;
}

void foo(T)(test!T t) { // works
}

void foo2(T)(aliasT!T t) { // doesn't work
}

int main(string[] args)
{
    test!(int) t;
    aliasT!(int) t2;
    foo(t);
    foo2(t2); // error
    return 0;
}


When foo2(t2) is called which takes an alias to test!T as argument I get the following error from dmd:

*(21): Error: template variant.foo2(T) does not match any function template declaration
*(21): Error: template variant.foo2(T) cannot deduce template function from argument types !()(test!(int))

I thought that aliasT!T and test!T have the same internal types and the compiler would be able deduce the template parameters. Am I missing something or is this a bug in DMD? This is a reduced test case from a piece of code where I tried to write an templated overload to std.variant.Algebraic.

Thanks,
André

On 12/24/2011 11:23 AM, André Stein wrote:
> Hi,
>
> I'm trying to write a template function which takes a templated alias to
> another type:
>
> struct test(T)
> {
> }
>
> template aliasT(T)
> {
> alias test!(T) aliasT;
> }
>
> void foo(T)(test!T t) { // works
> }
>
> void foo2(T)(aliasT!T t) { // doesn't work
> }
>
> int main(string[] args)
> {
> test!(int) t;
> aliasT!(int) t2;
> foo(t);
> foo2(t2); // error
> return 0;
> }
>
>
> When foo2(t2) is called which takes an alias to test!T as argument I get
> the following error from dmd:
>
> *(21): Error: template variant.foo2(T) does not match any function
> template declaration
> *(21): Error: template variant.foo2(T) cannot deduce template function
> from argument types !()(test!(int))
>
> I thought that aliasT!T and test!T have the same internal types and the
> compiler would be able deduce the template parameters. Am I missing
> something or is this a bug in DMD? This is a reduced test case from a
> piece of code where I tried to write an templated overload to
> std.variant.Algebraic.
>
> Thanks,
> André

IFTI can only deduce template parameters for symbols that are defined inside the template instantiation because then the symbol remembers the template parameters. IFTI cannot reverse-instantiate templates.