What's wrong in this snippet?

Question

I have no idea what's wrong with this snippet. I'm getting this error:

error: member function 'swap' not viable: 'this' argument has type 'const array', but function is not marked const

#include <algorithm>
#include <memory>
#include <iostream>
#include <array>

struct MyClass {
  std::array<float, 4> arr;  
  float carr[4];

  std::array<float, 4> getArrElement() {
    std::array<float, sizeof(carr) / sizeof(float)> out;
    return out;
  }

  void fun() {
    auto vec = { getArrElement(), getArrElement(), getArrElement() };
    std::reverse(vec.begin(), vec.end()); // <-- error line here
  }


};

int main()
{
    MyClass obj;
    obj.fun();
}

getArrElement isn't returning a const array. auto should be deduced to std::initializer_list but I also see no harm in that.

What's wrong?

Answer 1

As above, plus if the array is only used locally and never truncated, extended or moved, then by using the free functions begin() and end() we can avoid the overhead of allocating a vector....

    using element_type = decltype(std::declval<MyClass>().getArrElement());
    element_type vec[] = { getArrElement(), getArrElement(), getArrElement() };
    std::reverse(std::begin(vec), std::end(vec));