samedi 11 avril 2020

How to solve ambiguous declarations elegantly in C++11?

struct A
{
    A(int) {}
    A(std::initializer_list<int>) {}
};

template<typename T>
struct B
{
    B(A) {}
    B(std::initializer_list<T>) {}
};

int main()
{
    int n{};
    B   m1(A{n}); // error: call A::A(std::initializer_list<int>)
    B   m2(A(n)); // error: just a function declaration: B m2(A n);
}

As shown in the code above, I want to call B::B(A(int)) to construct an object of class B. I have two choices:

  1. B m1(A{n});
  2. B m1(A(n));

According to C++ Core Guidelines, the former is preferred.

However, B m1(A{n}); will call A::A(std::initializer_list<int>) rather than A::A(int), which is not intended. So, I have to use B m1(A(n));, but it is just a function declaration: B m2(A n);!

How to solve ambiguous declarations elegantly in C++11?

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