The below code example is just focused on constructors. Basically, my question concerns why the move constructor is not called, and if its because it is somehow "optimized away" by the compiler?
#include <iostream>
class Foo{
public:
int x_;
Foo(const int x = 0) : x_{x} {std::cout << "Default constructor used..." << std::endl;}
Foo(Foo&& f) : x_{f.x_} {std::cout << "Move constructor used..." << std::endl;}
Foo(const Foo& f) : x_{f.x_} {std::cout << "Copy constructor used..." << std::endl;}
};
Foo operator+(const Foo& f1, const Foo& f2)
{
Foo f; // default constructor used
f.x_ = f1.x_ + f2.x_;
return f;
}
int main()
{
Foo f1(3), f2(2); // two default constructor calls
Foo f = f1; // copy constructor gets called
Foo f_ = f1 + f2; // move is NOT called
std::cout << f.x_ << std::endl;
return 0;
}
Based on what I've read on move constructors the move constructor should have been called for the line
Foo f_ = f1 + f2;
but it is not.
f1 + f2
is not an lvalue, but an rvalue.
In fact, it appears like NO constructor is called for the construction of f_. The output of this program is:
Default constructor used...
Default constructor used...
Copy constructor used...
Default constructor used...
3
To me it looks like the construction of f_ is "hidden". I use g++ version 4.8.1 (64-bit) on Windows 8.1.
Appreciate any help. Thank you.
