C++ brace-initialize std::array requires move-constructor?

Question

I want to create a std::array of objects which are not movable and not copyable. Also the default constructor is deleted, there is just a constructor that takes a string argument.

#include <iostream>
#include <array>

class Foo {
 public:
  Foo() = delete;                // delete default constructor
  Foo(const Foo &obj) = delete;  // delete copy constructor
  Foo(Foo &&obj) = delete;       // delete move constructor

  Foo(std::string label) {
    label_ = label;
    std::cout << "Constructor " << std::endl;
  }

  ~Foo() {
    std::cout << "Destructor" << std::endl;
  }

 private:
  std::string label_;
};


int main() {
  std::array<Foo, 3> arr = {Foo("a"), Foo("b"), Foo("c")};
}

This is not accepted by the compiler, and I get an error like:

use of deleted function ‘Foo::Foo(Foo&&)’

If I explicitly implement a move-constructor like this:

Foo(Foo &&obj) {
  label_ = obj.label_;
  std::cout << "MOVE constructor" << std::endl;
}

everything compiles and runs, but from the output I see that the move-constructor is not used. So why does the compiler complain about the missing move-constructor, if it doesn't use it anyway? And how should I correctly initialize an array of non-copyable, non-movable objects?

C++ brace-initialize std::array requires move-constructor?

0 Answers0