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digitalmars.D.bugs - [Issue 8074] New: template-mixin example contradicts text

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8074

           Summary: template-mixin example contradicts text
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: websites
        AssignedTo: nobody puremagic.com
        ReportedBy: tim.dolores gmail.com



---
The text says:

"If two different mixins are put in the same scope, and each define a
declaration with the same name, there is an ambiguity error when the
declaration is referenced"

However, the example *does* compile with no error, and runs the Bar.func()
method. Here is the exact code I'm using:

$ cat mix08.d
import std.stdio, std.exception;

/*
   If two different mixins are put in the same scope, and each define a
   declaration with the same name, there is an ambiguity error when the
   declaration is referenced:
 */

mixin template Foo() {
    int x = 5;
    void func(int x) { writeln("Foo.func(), x = ", x); }
}

mixin template Bar() {
    int x = 4;
    void func() { writeln("Bar.func(), x = ", x); }
}

mixin Foo;
mixin Bar;

void main() {
    //writefln("x = %d", x); // error, x is ambiguous
    /*
       The call to func() is ambiguous because Foo.func and Bar.func are in
       different scopes.
     */
    func();             // error, func is ambiguous
}

$ dmd|grep DMD
DMD64 D Compiler v2.059
$ dmd -w mix08.d
$ ./mix08
Bar.func(), x = 4
$ 


I don't know if the text is wrong, or if DMD is wrong.

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May 09 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8074




---
I forgot to link to the exact spec page I'm talking about:

http://dlang.org/template-mixin.html

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May 09 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8074


Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrei erdani.com,
                   |                            |andrej.mitrovich gmail.com



20:22:31 PST ---
I seriously doubt we could implement this now without breaking code. Chances
are people are using it to inject multiple function overloads.

I think we'll simply have to edit that part out of the website. Andrei do you
agree?

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Feb 06 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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PST ---
We should fix this, it's clearly a crass error. We can't afford to arbitrarily
pick the last lexical declaration in case of an ambiguity.

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Feb 07 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
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09:53:20 PST ---


 We should fix this, it's clearly a crass error. We can't afford to arbitrarily
 pick the last lexical declaration in case of an ambiguity.


But there is no ambiguity, the two functions are:

void func(int x) { writeln("Foo.func(), x = ", x); }
void func() { writeln("Bar.func(), x = ", x); }

Neither of these can hijack one another.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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09:54:00 PST ---




 We should fix this, it's clearly a crass error. We can't afford to arbitrarily
 pick the last lexical declaration in case of an ambiguity.


 
 But there is no ambiguity, the two functions are:
 
 void func(int x) { writeln("Foo.func(), x = ", x); }
 void func() { writeln("Bar.func(), x = ", x); }
 
 Neither of these can hijack one another.


Edit: Well except the case of taking the address of such a function which could
prove problematic.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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I think there is no ambiguity for current behavior.

I can explain it based on the 'overload set resolution rule'.

Please regard these mixin declarations as two import statements.

  mixin Foo;
  mixin Bar;
  void main() { func(); }

Can be considered to:

  import foo;
  import bar;
  void main() { func(); }

And each module contains following declarations.

  module foo;  // ---
  int x = 5;
  void func(int x) { writeln("Foo.func(), x = ", x); }

  module bar;  // ---
  int x = 4;
  void func() { writeln("Bar.func(), x = ", x); }

Finally, the 'func()' is resolved to the call of bar.func.

"compiler will resolve an ambiguous mixin-ed symbol by regarding it as overload
set.." - This is much reasonable and consistent rule. If 'foo' is called with
some arguments but cannot eliminate the ambiguity, it will be error. Otherwise
simply will succeed to call.

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Feb 14 2013
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8074


Martin Nowak <code dawg.eu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |code dawg.eu





 I can explain it based on the 'overload set resolution rule'.


Yes, according to http://dlang.org/template-mixin.html these form an overload
set and only one of the sets has a match.



 Edit: Well except the case of taking the address of such a function which
could > prove problematic.


No problem here, you just have to specify the function type.

void foo() {}
void foo(int) {}

void main()
{
    void function() a1 = &foo;
    void function(int) a2 = &foo;
    auto b1 = cast(void function())&foo;
    auto b2 = cast(void function(int))&foo;
    assert(cast(void*)a1 !is cast(void*)a2);
    assert(a1 is b1);
    assert(a2 is b2);
}

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May 20 2013