Why are copy constructors unnecessary for immutable objects?

Question

Why are copy constructors unnecessary for immutable objects? Please explain this for me.

Answer 1

Because the value cannot change, it's every bit as good to reference the same object in all cases, there's no need to have an "extra copy", so to speak.

Answer 2

This is a language dependent question especially with respect to lifetime. For a moment lets forget about those.

Copy constructors are valuable in that they allow for you to take one object and create a completely independent copy of it. This is valuable in that you can now modify the second object independent of the first. Or a component can create a private copy to protect itself from other components changing the object out from under it.

Immutable objects are unchangeable. There is no value in creating a copy of an object that won't change.

Now lets thing about lifetime again. In languages like C++ copy constructors also allow you to work around memory / lifetime issues. For example if I'm writing an API which takes a SomeType* and I want to keep it around longer than the lifetime of my method. In C++ the most reliable way to do this is to create a copy of the object via a copy constructor.