[llvm-bugs] [Bug 31406] New: CRTP with inhered template member function is not included in overload resolution

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Dec 16 04:34:56 PST 2016


https://llvm.org/bugs/show_bug.cgi?id=31406

            Bug ID: 31406
           Summary: CRTP with inhered template member function is not
                    included in overload resolution
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: pedro.ferreira at imgtec.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following C++ source file compiles fine:

=======
#include <type_traits>
#include <cstdint>

template<typename Base, typename A>
class EnumAlias
{
public:
    template<typename E, typename std::enable_if<std::is_enum<E>::value>::type*
= nullptr>
    void operator()(E& e)
    {
        Base& base = *static_cast<Base*>(this);
        A& a = (A&)(e);
        base(a);
    }
};

class Base;
typedef EnumAlias<Base, uint32_t> EnumAliasU32;

class Base : public EnumAliasU32
{
public:
    using EnumAliasU32::operator();

    template<typename T, typename
std::enable_if<std::is_fundamental<T>::value>::type* = nullptr>
    void operator()(const T& e)
    {
        //something, whatever
    }
};

enum SomeEnumTy {};

void Use()
{
    SomeEnumTy e;

    Base b;
    b(e);
}
========



However, if one is to remove "const" from Base::operator(), clang fails with

=======
CRTP.cpp:39:2: error: no matching function for call to object of type 'Base'
        b(e);
        ^
CRTP.cpp:25:47: note: candidate template ignored: disabled by 'enable_if' [with
T = SomeEnumTy]
        template<typename T, typename
std::enable_if<std::is_fundamental<T>::value>::type* = nullptr>
                                                     ^
1 error generated.
=======

G++ accepts the code. Is the input source incorrect?
It seems on the second, the inherited function does not participate in overload
resolution (even though it does when "const" is specified).

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