What are the use cases for having a function return by const value for non-builtin type?

Question

Recently I have read that it makes sense when returning by value from a function to qualify the return type const for non-builtin types, e.g.:

const Result o         


        

Answer 1

There is no benefit when returning by value. It doesn't make sense.

The only difference is that it prevents people from using it as an lvalue:

class Foo
{
    void bar();
};

const Foo foo();

int main()
{
    foo().bar(); // Invalid
}