Not calling constructor of object that instantiate by returned value in C++ [duplicate]

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• What are copy elision and return value optimization? 4 answers

Why constructor of class that is instantiate by returned value of a function, not be called?

For example, I wrote this code: a temp class with copy and move constructor and writing a string in destructor and I expected when an object created by output of a function, which is created in it's scope, copy constructor must be called but nothing occurs.

template <typename T>
class temp {
public:
    T a;
    temp() = default;
    temp (const temp& t) {
       cout<<"copy cons "<<endl;
       a = t.a;
    }

    temp (const temp<int>&& t) noexcept {
        cout<<"copy move1 "<<endl;
        a = t.a;
    }

    temp (temp&& t) noexcept {
        cout<<"copy move2 "<<endl;
        a = t.a;
    }

    temp(int _a ) : a(_a) {
    }
    ~temp() {
        cout<<"~~ temp "<<this<<" "<<a<<endl;
    }

};

temp<int> ttt(int b) {
    temp<int> bb(b);
    cout<<"adrs: "<<&bb<<endl;
    return bb;
}

temp<int> tt(int b) {
    temp<int> bb = ttt(b);
    cout<<"adrs: "<<&bb<<endl;
    return bb;
}

temp<int> t = tt(2);

int main ()
{
    cout<<"adrs: "<<&t<<endl;
    return 0;   
}