asma22 asma22 - 6 months ago 48
Objective-C Question

What is Protocol Oriented Programming in Swift? What added value does it bring?

From Apple's own website: "At the heart of Swift's design are two incredibly powerful ideas: protocol-oriented programming and first class value semantics."

Can someone please elaborate what exactly is protocol oriented programming, and what added value does it bring?

I have read this and watched the Protocol-Oriented Programming in Swift video, but coming from an Objective-C background still haven't understood it. I kindly ask for a very plain English answer along with code snippets & technical details about how it's different from Objective-C.

Just one of the confusions I have is using

<tableViewDelegate, CustomDelegate>
Couldn't we also conform to multiple protocols in Objective-C as well? So again how is Swift new?

Answer

The primary point of POP over OOP is that is prefers composition over inheritance. There are several benefits to this.

In large inheritance hierarchies, the ancestor classes tend to contain most of the (generalized) functionality, with the leaf subclasses making only minimal contributions. The issue here is that the ancestor classes end up doing a lot of things. For example, a Car drives, stores cargo, seats passengers, plays musics, etc. These are many functionalities that are each quite distinct, but they all get indivisibly lumped into the Car class. Descendants of Car, such as Ferrari, Toyota, BMW, etc. all make minimal modifications to this base class.

The consequence of this is that tere is reduced code reuse. My BoomBox also plays music, but it's not a car. Inheriting the music-playing functionality from Car isn't possible.

What Swift encourages instead is that these large monolithic classes be broken down into a composition of smaller components. These components can then be more easily reused. Both Car and BoomBox can use MusicPlayer.

Swift offers multiple features to achieve this, but the most important by far are protocol extensions. They allow implementation of a protocol to exist separate of its implementing class, so that many classes may simply implement this protocol and instantly gain its functionality.

To answer your "subquestions":

  1. What do you mean?
  2. Yes, Objective-C supports multiple protocol conformance. However, POP was not a part of the convention for the language. A large hinderance to this is that you couldn't provide default implementations of Protocols.
  3. Structs/Enums being able to conform to protocols is a nice feature, but not ultimately necessary for POP.
  4. I'm not sure what you mean here, either.