The code to reproduce the problem consists of 3 modules:

mix.d:

module mix;

mixin template A( alias x) {

  string a () {
    return x;
  }
}

====================
aux.d:

module aux;

import mix;

mixin A!("a in aux") X;
string b () { return "b in aux"; }

====================
main.d:

module main;

import aux;
import mix;
import std.stdio;

mixin A!("a in main") X;
string b () { return "b in main"; }

void main () {
  writefln( "a: %s", X.a );  // Line 1
  //writefln( "a: %s", a );  // Line 2
  writefln( "b: %s", b ); // Line 3
}

I run it with: dmd -run main.d aux.d mix.d

Line 1 works. Line 3 works. Line 2 fails with:
main.d(13): Error: main.A!("a in main").a at mix.d(5) conflicts with aux.A!
("a in aux").a at mix.d(5)

If I omit mixin identifier ("X"), there is no way I can make the call to "a" work without prepending module name.

My question is: why calling a function with the same name (from different
modules) works when:
- it is just a regular function
- it is a mixed-in function with mixin identifier (even though the
identifier is ambiguous)

and it doesn't when it's a mixed-in function with no mixin identifier.

My first impression is that either both line 1 and 2 should work or neither of them should work. It's no surprise to me that line 3 works (and it matches the documentation), so I basically included that just for reference.

-- 
Marek Janukowicz

On Sunday, 15 September 2013 at 18:31:30 UTC, Marek Janukowicz wrote:
> The code to reproduce the problem consists of 3 modules:
>
> mix.d:
>
> module mix;
>
> mixin template A( alias x) {
>
>   string a () {
>     return x;
>   }
> }
>
> ====================
> aux.d:
>
> module aux;
>
> import mix;
>
> mixin A!("a in aux") X;
> string b () { return "b in aux"; }
>
> ====================
> main.d:
>
> module main;
>
> import aux;
> import mix;
> import std.stdio;
> 
> mixin A!("a in main") X;
> string b () { return "b in main"; }
>
> void main () {
>   writefln( "a: %s", X.a );  // Line 1
>   //writefln( "a: %s", a );  // Line 2
>   writefln( "b: %s", b ); // Line 3
> }
>
> I run it with: dmd -run main.d aux.d mix.d
>
> Line 1 works. Line 3 works. Line 2 fails with:
> main.d(13): Error: main.A!("a in main").a at mix.d(5) conflicts with aux.A!
> ("a in aux").a at mix.d(5)
>
> If I omit mixin identifier ("X"), there is no way I can make the call to "a"
> work without prepending module name.
>
> My question is: why calling a function with the same name (from different
> modules) works when:
> - it is just a regular function
> - it is a mixed-in function with mixin identifier (even though the
> identifier is ambiguous)
>
> and it doesn't when it's a mixed-in function with no mixin identifier.
>
> My first impression is that either both line 1 and 2 should work or neither
> of them should work. It's no surprise to me that line 3 works (and it
> matches the documentation), so I basically included that just for reference.

Currently this is not a bug.

Looking from the module 'main', the mixin identifier 'X' declared in main.d is *closer* than the 'X' declared in aux.d, because the latter exists beyond the module import boundary.
Therefore, the use of 'X' in main.d would prefere the `mixin A!("a in main") X`.

On the other hand, when the name search, all mixed-in symbols are treated as if they are just imported at the mixed-in scope.
Therefore, even from main.d, the two mixed-in functions 'a' have same closeness, and the call is ambiguous because they have exactly same signature.

Kenji Hara

Kenji Hara wrote:
> Currently this is not a bug.
> 
> Looking from the module 'main', the mixin identifier 'X' declared
> in main.d is *closer* than the 'X' declared in aux.d, because the
> latter exists beyond the module import boundary.
> Therefore, the use of 'X' in main.d would prefere the `mixin
> A!("a in main") X`.

I get this one - if X was eg. a class and I was calling it's static member it would work the same way.

> On the other hand, when the name search, all mixed-in symbols are treated as if they are just imported at the mixed-in scope.

Could you please elaborate a bit more or point me to some documentation where this is described? If the mixins are imported at mixed-in scope, my understanding would be the one in 'main' is closer than the one in 'aux'.

> Therefore, even from main.d, the two mixed-in functions 'a' have same closeness, and the call is ambiguous because they have exactly same signature.


-- 
Marek Janukowicz