Consider the following:
class A {
public:
const int c; // must not be modified!
A(int _c)
: c(_c)
{
// Nothing here
}
A(const A& copy)
: c(copy.c)
{
// Nothing here
}
};
int main(int argc, char *argv[])
{
A foo(1337);
vector<A> vec;
vec.push_back(foo); // <-- compile error!
return 0;
}
Obviously, the copy constructor is not enough. What am I missing?
EDIT:
Ofc. I cannot change this->c
in operator=()
method, so I don't see how operator=()
would be used (although required by std::vector
).
I'm not sure why nobody said it, but the correct answer is to drop the const
, or store A*
's in the vector (using the appropriate smart pointer).
You can give your class terrible semantics by having "copy" invoke UB or doing nothing (and therefore not being a copy), but why all this trouble dancing around UB and bad code? What do you get by making that const
? (Hint: Nothing.) Your problem is conceptual: If a class has a const member, the class is const. Objects that are const, fundamentally, cannot be assigned.
Just make it a non-const private, and expose its value immutably. To users, this is equivalent, const-wise. It allows the implicitly generated functions to work just fine.