• =?ISO-8859-1?Q?Andr=E9_Stein?= (35/35) Dec 24 2011 Hi,
• Timon Gehr (4/39) Dec 24 2011 IFTI can only deduce template parameters for symbols that are defined

=?ISO-8859-1?Q?Andr=E9_Stein?= writes:

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,
Andr�

Timon Gehr <timon.gehr gmx.ch> writes:

On 12/24/2011 11:23 AM, Andr� 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,
 Andr�

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.