swift语言点评二十一-协议

定义有什么，及哪些必须实现。

A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality.

Property Requirements

The protocol doesn’t specify whether the property should be a stored property or a computed property—it only specifies the required property name and type.

1. protocol SomeProtocol {
2. var mustBeSettable: Int { get set }
3. var doesNotNeedToBeSettable: Int { get }
4. }

If you mark a protocol instance method requirement as mutating, you don’t need to write the mutatingkeyword when writing an implementation of that method for a class. The mutating keyword is only used by structures and enumerations.

Class-Only Protocols

You can limit protocol adoption to class types (and not structures or enumerations) by adding the AnyObjectprotocol to a protocol’s inheritance list.

1. protocol SomeClassOnlyProtocol: AnyObject, SomeInheritedProtocol {
2. // class-only protocol definition goes here

协议联合体作为参量

1. func wishHappyBirthday(to celebrator: Named & Aged) {
2. print("Happy birthday, \(celebrator.name), you're \(celebrator.age)!")
3. }
4. let birthdayPerson = Person(name: "Malcolm", age: 21)
5. wishHappyBirthday(to: birthdayPerson)