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From: pawig@hildesheim.sgh-net.de To: gcc-gnats@gcc.gnu.org Subject: c++/8875: Ambiguities in mixed template hierarchies Date: Sun, 08 Dec 2002 10:56:00 -0000 [thread overview] Message-ID: <20021208185505.15025.qmail@sources.redhat.com> (raw) [-- Warning: decoded text below may be mangled, UTF-8 assumed --] [-- Attachment #1: Type: text/plain, Size: 2931 bytes --] >Number: 8875 >Category: c++ >Synopsis: Ambiguities in mixed template hierarchies >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: rejects-legal >Submitter-Id: net >Arrival-Date: Sun Dec 08 10:56:00 PST 2002 >Closed-Date: >Last-Modified: >Originator: Stefan Große Pawig >Release: gcc (GCC) 3.2.1 (also with 3.2) >Organization: >Environment: Linux rigel 2.4.18 #5 Thu Aug 1 22:19:10 CEST 2002 i686 unknown >Description: The following code snippet (see below) exercises a base class template with concrete and pure virtual methods as well as general and specialized derived templates, which provide implementations for the pure virtual methods. Spezializations are provided for void* as well as for pointers in general, which builds on the void* spezialization via private inheritance. The problem occurs when one of the concrete methods of the base class is called on an instantiation of the derived template for pointers (Derviced<int*> in the sample code): the compiler complains that the concrete member is ambiguous (line 37). Using explicit qualification works for Base<int*>::doThat() but fails for Base<void*>::doThat() as expected (line 39), so why does the compiler regard the unqualified call as ambiguous? Am I missing something here? Or is this an effect of the "Two stage lookup in templates is not implemented." as stated on the "GCC Bugs" page? >How-To-Repeat: pawig@rigel:~/src > cat ctest1.cc // Base class template template <typename T> class Base { public: virtual T doThis() const = 0; bool doThat() const { return doThis() == T(); } }; // General Derived class template template <typename T> class Derived : public Base<T> { public: T doThis() const { return T(); } }; // Derived specialized for void* template<> class Derived<void*> : public Base<void*> { public: void* doThis() const { return reinterpret_cast<void*>(0x0badbeef); } }; // Derived specialized for any pointer template <typename T> class Derived<T*> : public Base<T*>, private Derived<void*> { public: T* doThis() const { return static_cast<T*>(Derived<void*>::doThis()); } }; int main() { Derived<int*> d; bool b1 = d.doThat(); // Line 37 bool b2 = d.Base<int*>::doThat(); bool b3 = d.Base<void*>::doThat(); // Line 39 return 0; } pawig@rigel:~/src > g++ -c ctest1.cc ctest1.cc: In function `int main()': ctest1.cc:37: request for member `doThat' is ambiguous ctest1.cc:7: candidates are: bool Base<T>::doThat() const [with T = void*] ctest1.cc:7: bool Base<T>::doThat() const [with T = int*] ctest1.cc:39: `Base<void*>' is an inaccessible base of `Derived<int*>' >Fix: Workaround: Instead of deriving Derived<T*> privately from Derived<void*>, just put a Derived<void*> data meber into the Derived<T*> template. >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2002-12-08 18:56 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-12-08 10:56 pawig [this message] 2002-12-09 11:42 bangerth 2002-12-10 2:09 nathan
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