[LLVMbugs] [Bug 21772] New: Template type conversion operator not used leading to erroneous compilation error

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21772

            Bug ID: 21772
           Summary: Template type conversion operator not used leading to
                    erroneous compilation error
           Product: clang
           Version: 3.5
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mail at endlessvoid.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following code looks like valid C++ 11 but fails with error

"no matching constructor for initialization of 'Ptr<Shape>'"

It compiles ok on gcc 4.9. Based on example code taken from Stroustrup's The
C++ Programming Language 4th edition, pp 764-765.

template <typename T>
struct Ptr {
    Ptr(T* pp) : p{pp} { }

    template <typename U>
    explicit operator Ptr<U>(); // Convert Ptr<T> to Ptr<U>
private:
    T* p;
};

template<typename T>
template<typename U>
Ptr<T>::operator Ptr<U>()
{
    return Ptr<U>{p};
}

struct Shape {};
struct Circle : Shape {};

int main()
{
    Circle c;
    Ptr<Circle> pc{&c};
    // The following instantiation causes the
    // error. Ptr<Circle>::operator Ptr<Shape>() should be getting
    // implicitly called on the argument pc, before the result is used
    // to call Ptr<Shape>'s default copy constructor.
    Ptr<Shape> ps{pc};
}

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