Question

I have two getter members:

Node* prev() { return prev_; }
int value()  { return value_ }

Please note the lack of const identifiers (I forgot them, but now I want to know why this won’t work). I am trying to get this to compile:

Node(Node const& other) : prev_(other.prev()), value_(other.value()) { }

The compiler rejects this. I thought that C++ allows non-const to const conversion in function parameters, such as:

{
   Foo(int bar);
}

Foo(const int bar)
{
   //lala
}

Why won’t it let me do the same thing with a copy constructor? The const identifier means I promise not to change anything, so why would it matter if I get my value from a const or non-const source?

Answer 1

You’re not trying to do a non-const to const conversion. You’re attempting to call two methods which are not const an a const reference (calls to prev and value). This type of operation is strictly forbidden by const semantics.

What you could do instead is use the fields prev_ and value_ directly. Because it’s a member of the same type you can access privates which will be available on the const object.