Comment by not2b

Unfortunately in C++, the compiler is not allowed to assume that if it passes a const reference to a function, that function will not change the object. The function is allowed to cast away const and modify the object. I'm not happy that they did it that way; I would have preferred it if cast-away-const were more restricted (for example, allowed when calling a child function that takes a char* but doesn't modify the pointed-to C string), with the idea being that if a function has only a pointer to const or a reference for a const object, it has read permission on the object and lacks write permission. But that isn't how the language works.