C++11: Difference between v = { } and v { }

Question

I would like to ask if there is any difference between following two statements:

// C++11
std::vector<int> d {1, 2, 3};
std::vector<int> d = {1, 2, 3};

In both cases the sequence constructor gets invoked:

class A {
public:
  int a;

  A() {
    cout << "default constructor" << endl;
  };

  A(const A& other) {
    cout << "copy constructor" << endl;
  };

  A& operator =(const A& other) {
    cout << "assignment operator" << endl;
  }

  A(std::initializer_list<int> e) {
    cout << "sequence constructor" << endl;
  };

  A& operator =(std::initializer_list<int> e) {
    cout << "initializer list assignment operator" << endl;
  }
};

int main(int argc, char** argv) {

  A a {1, 2}; // sequence constructor
  A b = {1, 2}; // sequence constructor
  b = {1, 2}; // initializer list assignment operator
}

Answer 1

Doing e.g.

A myA{...};

will always invoke the appropriate constructor.

But doing

A myA = ...;

will do different things depending on the expression on the right-hand side of the assignment, as it might invoke the copy-constructor instead. Or optimize it out with copy-elision.

Also, if you have an array you have to use the assignment syntax.