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digitalmars.D.bugs - [Issue 8146] New: Potentially ambiguous overloaded call

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8146

           Summary: Potentially ambiguous overloaded call
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



This is just a potential enhancement request. It's not an enhancement request
because I am not sure about it.

A thread started by Andrej Mitrovic on D.learn:
http://forum.dlang.org/thread/mailman.1043.1337863952.24740.digitalmars-d-learn puremagic.com

In dmd 2.060alpha this code compiles and doesn't assert at run-time, so it
calls the second overload:


struct Foo {}
void test(void* test) { assert(0); }
void test(Foo* test) {}
void main() {
    test(null);
}


As Andrej comments, shouldn't this be considered an ambiguous call, and refused
at compile time?

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8146






 This is just a potential enhancement request. It's not an enhancement request
 because I am not sure about it.
 
 A thread started by Andrej Mitrovic on D.learn:
 http://forum.dlang.org/thread/mailman.1043.1337863952.24740.digitalmars-d-learn puremagic.com
 
 In dmd 2.060alpha this code compiles and doesn't assert at run-time, so it
 calls the second overload:
 
 
 struct Foo {}
 void test(void* test) { assert(0); }
 void test(Foo* test) {}
 void main() {
     test(null);
 }
 
 
 As Andrej comments, shouldn't this be considered an ambiguous call, and refused
 at compile time?


I think, no.

First, test(Foo*) is specialized than test(void*), because Foo* is convertible
to void*, but opposite isn't.

Next, a null literal has the typeof(null) and it is *most specialized type* of
all reference types. Then typeof(null) is a specialized type than Foo*.

So, with the call 'test(null)', overload resolution will select more
specialized test(Foo*) than test(void*).

Following is a similar case by the class hierarchy.

class B{}      // like void*
class C : B{}  // like Foo*
class D : C{}  // like typeof(null)
void foo(B o){}
void foo(C o){}
void main() {
    foo(new D); // calls foo(C)
}

As far as I know, this rule is same as C++.

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May 24 2012
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8146


bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID






 As far as I know, this rule is same as C++.


C++ is often not not a good model to copy, but I trust your judgment and
knowledge, so I close this ER as invalid.

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