Does this copy the vector?

Question

If I have the following code, is the vector copied?

std::vector x = y.getTheVector();

or would it depend on whether the return t

Answer 1

std::vector x = y.getTheVector();

This is copy-initialization. There are three possible scenarios:

1. The return value of getTheVector() is a lvalue reference. In this case, the copy constructor is always invoked.
2. The return value of getTheVector() is a temporary. In this case, the move constructor may be called, or the move/copy may be completely elided by the compiler.
3. The return value is a rvalue reference (usually a terrible idea). In this case, the move constructor is called.

For this line,

 std::vector& x = y.getTheVector();

This only compiles if getTheVector returns a lvalue reference; a temporary cannot be bound a non-const lvalue reference. In this case, no copy is ever made; but the lifetime problem may be tricky.