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> Hello,
>
> If anyone can give me some insight as to why this code fails to
> compile, I would be most appreciative. I have only been able to test
> it with gcc 3.4.4 and gcc 4.2.1, which both fail with different errors
> (details below).
>
> //////// begin test_bug.cpp
>
> // Standard Type2Type from Alexandrescu's Modern C++ Design
> template<typename T>
> struct Type2Type
> {
> typedef T OriginalType;
> };
>
> // Base for mix-in classes
> template<typename Mixin>
> struct MixinBase
> {
> virtual ~MixinBase() {}
> virtual void mixinVirtual() {}
>
> static void mixinStatic(Type2Type<Mixin>) {}
> };
>
> struct MixinA
> : public MixinBase<MixinA>
> {
> };
>
> struct MixinB
> : public MixinBase<MixinB>
> {
> };
>
> // Base for mix-in classes in an object
> template<typename ObjType, typename Mixin>
> struct ObjMixin
> : public Mixin
> {
> void mixinVirtual()
> {
> // Call mixinStatic in our base object (the one that derives
> from us)
> // This should call the function defined in ObjType itself if
> one exists
> // or the default in MixinBase if not (behavior similar to a
> virtual function
> // but without the actual dynamic dispatch).
> ObjType::mixinStatic(Type2Type<Mixin>());
> }
> };
>
> // Object composed of two mix-in classes
> struct TestObj
> : public ObjMixin<TestObj, MixinA>
> , public ObjMixin<TestObj, MixinB>
> {
>
> } testInstance;
>
> //////// end test_bug.cpp
>
> g++ 4.2.1 rejects this with the following output:
> ----------
> % g++ test_bug.cpp
> test_bug.cpp: In member function 'void ObjMixin<ObjType,
> Mixin>::mixinVirtual() [with ObjType = TestObj, Mixin = MixinA]':
> test_bug.cpp:44: instantiated from here
> test_bug.cpp:35: error: reference to 'TestObj::mixinStatic' is
> ambiguous
> test_bug.cpp:15: error: candidates are: static void
> MixinBase<Mixin>::mixinStatic(Type2Type<Mixin>) [with Mixin = MixinB]
> test_bug.cpp:15: error: static void
> MixinBase<Mixin>::mixinStatic(Type2Type<Mixin>) [with Mixin = MixinA]
> test_bug.cpp: In member function 'void ObjMixin<ObjType,
> Mixin>::mixinVirtual() [with ObjType = TestObj, Mixin = MixinB]':
> test_bug.cpp:44: instantiated from here
> test_bug.cpp:35: error: reference to 'TestObj::mixinStatic' is
> ambiguous
> test_bug.cpp:15: error: candidates are: static void
> MixinBase<Mixin>::mixinStatic(Type2Type<Mixin>) [with Mixin = MixinB]
> test_bug.cpp:15: error: static void
> MixinBase<Mixin>::mixinStatic(Type2Type<Mixin>) [with Mixin = MixinA]
> ----------
>
> This would at least appear to be wrong, since the different values for
> Mixin (MixinA and MixinB) should disambiguate the call.
>
> g++ 3.4.4 rejects it with the following output:
> ----------
>> g++ test_bug.cpp
>
> test_bug.cpp: In member function `void ObjMixin<ObjType,
> Mixin>::mixinVirtual() [with ObjType = TestObj, Mixin = MixinA]':
> test_bug.cpp:40: instantiated from here
> test_bug.cpp:32: error: `mixinStatic' is not a member of `TestObj'
> test_bug.cpp: In member function `void ObjMixin<ObjType,
> Mixin>::mixinVirtual() [with ObjType = TestObj, Mixin = MixinB]':
> test_bug.cpp:40: instantiated from here
> test_bug.cpp:32: error: `mixinStatic' is not a member of `TestObj'
> ----------
>
> Again this seems wrong, removing ObjMixin<TestObj, MixinB> from the
> definition of TestObj results in correct compilation under both
> versions, so clearly mixinStatic is found as a member of TestObj in
> some cases.
>
> Thanks in advance for any insight into what could be going on here.
Fails Comeau online compiler as well but the error messages may
be a bit clearer:
Comeau C/C++ 4.3.9 (Mar 27 2007 17:24:47) for ONLINE_EVALUATION_BETA1
Copyright 1988-2007 Comeau Computing. All rights reserved.
MODE:strict errors C++ C++0x_extensions
"ComeauTest.c", line 34: error: "MixinBase<Mixin>::mixinStatic [with
Mixin=MixinA]"
is ambiguous
ObjType::mixinStatic(Type2Type<Mixin>());
^
detected during instantiation of "void ObjMixin<ObjType,
Mixin>::mixinVirtual() [with ObjType=TestObj,
Mixin=MixinA]"
"ComeauTest.c", line 34: error: "MixinBase<Mixin>::mixinStatic [with
Mixin=MixinA]"
is ambiguous
ObjType::mixinStatic(Type2Type<Mixin>());
^
detected during instantiation of "void ObjMixin<ObjType,
Mixin>::mixinVirtual() [with ObjType=TestObj,
Mixin=MixinB]"
2 errors detected in the compilation of "ComeauTest.c".
In strict mode, with -tused, Compile failed
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