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Alexander Soare
Alexander Soare

Reputation: 3247

Swift: Do protocols even have a real purpose?

I'm wondering why protocols are used in swift. In every case I've had to use one so far (UICollectionViewDelegate, UICollectionViewDataSource) I've noted that they don't even have to be added to the class declaration for my code to work. All they do is make it such that your class needs to have certain methods in it so that it can compile. Beats me why this is useful other then as a little post it note to help you keep track of what your classes do.

I'm assuming I'm wrong though. Would anyone care to point out why to me please?

Upvotes: 2

Views: 944

Answers (2)

Joseph Lord
Joseph Lord

Reputation: 6504

It allows flexible linkage between parts of code. Once the protocol is defined it can be used by code that doesn't need to know what will be done when the methods are called or exactly what object (or struct or enum) is actually being used. An alternative approach could be setting callbacks or blocks but by using a protocol as complete set of behaviours can be grouped and documented.

Some other code will typically create the concrete instance and pass it to the code expecting the protocol (sometimes the concrete instance will pass itself). In some cases neither the implementation of the code using it need to be aware of each other and it can all be set up by some other code to keep it reusable and testable.

It might be possible to do this in some languages by duck typing which is to say that a runtime inspection could allow a object to act in such a context without particular declaration but this is probably not possible to do at compile time in all cases and it could also be error prone if worked out implicitly.

Upvotes: 0

Robert Harvey
Robert Harvey

Reputation: 180787

A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol doesn’t actually provide an implementation for any of these requirements—it only describes what an implementation will look like.

So it's basically an interface, right?

You use an interface when you want to define a "contract" for your code. In most cases, the purpose of this is to enable multiple implementations of that contract. For example, you can provide a real implementation, and a fake one for testing.

Further Reading
Protocols
What is the point of an Interface?

Upvotes: 4

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