How Object Oriented Programming and Functional programming can be used together?

Question

Scala claims than OO and FP can be combined. I wonder how this can be achieved in practice. I mean object can change, so making them immutable means i have to create a new object whenever something changes right? This doesn't seem too effective to me.

By the way, if i make external reference to an object property from a function, doesn't it hurts referential transparency?

Answer 1

Don't think of this as one paradigm imposing restrictions on the other but as how can one take the best of both paradigms.

As a simple example:

Objects have functions which can be internal to an object. Now the internal functions can be immutable within an object and those results of a function can be used to change the state of a object.

Thinking at a different level one can use functions to create a library that can be used by objects.

How I like to make the best of both is I tend to make libraries (modules) for the more abstract processing using a functional language and then use OO languages for the layers closer to human and external processing. This is not a hard and fast rule but a guideline from where I start.

• gabox01: By internal function you mean method :)
• gabox01: Do you mean that if a pure function takes an object as parameter, the first thing it should do is to clone it?
• Guy Coder: By internal function you mean method. Yes.
• Guy Coder: Do you mean that if a pure function takes an object as parameter, the first thing it should do is to clone it? No. Think of it like this; the function would pull the object off the stack, change it, then store the result (possibly a modified object) on the stack.