jeudi 23 avril 2015

Overload resolution difference between gcc and clang involving move constructor and 'Derived(Base&&)' constructor

GCC (tested with 4.9) accepts the following testcase:

struct Base {};

struct Derived : Base {
    Derived();
    explicit Derived(const Derived&);
    explicit Derived(Derived&&);
    explicit Derived(const Base&);
    Derived(Base&&);
};

Derived foo() {
  Derived result;
  return result;
}

int main() {
  Derived result = foo();
}

Clang (tested with 3.5) rejects it with the following error message:

test.cpp:13:10: error: no matching constructor for initialization of 'Derived'
  return result;
         ^~~~~~
test.cpp:8:5: note: candidate constructor not viable: no known conversion from 'Derived' to 'Base &&' for 1st argument
    Derived(Base&&);
    ^
test.cpp:4:5: note: candidate constructor not viable: requires 0 arguments, but 1 was provided
    Derived();
    ^

Who is right?

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