[LLVMbugs] [Bug 8263] New: Incorrect constructor name resolution

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu Sep 30 14:33:37 PDT 2010


           Summary: Incorrect constructor name resolution
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: schaub-johannes at web.de
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com

The following looks well-formed

struct A { 
  typedef A type;

// The following is SFINAE'ed out if T is A
template<typename T>
void f(typename T::A*);

// The following is not when T is A
template<typename T>
void f(typename T::type*);

int main() {

Clang says

main1.cpp:14:3: error: call to 'f' is ambiguous
main1.cpp:7:6: note: candidate function [with T = A]
void f(typename T::A*);
main1.cpp:11:6: note: candidate function [with T = A]
void f(typename T::type*);

And the Standard says at [class.qual]p2

"In a lookup in which the constructor is an acceptable lookup result and the
nested-name-specifier nominates a class C [...]  if the name specified after the
nested-name-specifier, when looked up in C, is the injected-class-name of C
[...] the name is instead considered to name the constructor of class C.".

A constructor is an acceptable lookup result for a "typename ...", since
function names are not ignored in a typename-specifier during lookup (see the
clearifying note at p2). Clang restricts that replacement to situations where
constructors can be declared only, though. 

The above code is accepted by comeau online compiler. Usually I found GCC
rejects all the cases I expect it to for the constructor name replacement (i.e
it acts not like clang in this regard), but GCC also rejects the above code.
But that is because GCC ignores function names in a typename-specifier lookup,
not because it wouldn't do the constructor-name replacement in general.

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