Could a smart compiler do all the things std::move does without it being part of the language?

Question

This is a bit theoretical question, but although I have some basic understanding of the std::move Im still not certain if it provides some additional functionality to the la

Answer 1

Doing this the way you suggest is a lot more complicated than necessary:

std::string s1="STL";
std::string s2(s1);
std::cout << s1 <

In this case, it is fairly sure that a copy is meant. But if you drop the last line, s1 essentially ends its lifetime after the construction of s2.

In a reference counted implementation, the copy constructor for std::string will only increment the reference counter, while the destructor will decrement and delete if it becomes zero.

So the sequence is

1. (inlined std::string::string(char const *))
   1. determine string length
   2. allocate memory
   3. copy string
   4. initialize reference counter to 1
   5. initialize pointer in string object
2. (inlined std::string::string(std::string const &))
   1. increment reference counter
   2. copy pointer to string representation

Now the compiler can flatten that, simply initialize the reference counter to 2 and store the pointer twice. Common Subexpression Elimination then finds out that s1 and s2 keep the same pointer value, and merges them into one.

In short, the only difference in generated code should be that the reference counter is initialized to 2.