I’m trying to understand the exact behavior of object initialization in C++ when using a function that returns a reference to *this. Consider the following generic code:

class T {
public:
    T& func() { /* do something */ return *this; }
};

const T obj = T().func();

And a concrete example using std::string:

const std::string fullName = std::string(firstName).append(" ").append(lastName);

Does the fact that the methods return a reference to a temporary object affect whether the copy or move constructor is used?

My understanding is that the copy constructor is called because the functions return an lvalue reference and the compiler can not know that it is from a temporary object.

However, I’m curious about potential optimizations and whether there are any nuances I’m missing.

I currently use

const T obj = std::move(T().func());

and in case of std::string I would use

const std::string fullName = std::string(firstName) + " " + std::string(lastName);