swift 学习（7）Methods

Methods, as you’ve already seen, are merely functions that reside inside a structure.

Comparing methods to computed properties
使用计算属性还是使用方法，可以使用下面的逻辑进行判断。

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mutating methods

Methods in structures cannot change the values of the instance without being marked as mutating. You can imagine a method in the Date structure that advances to the next day:

mutating func advance() {
    day += 1 
}

Type methods

Like type properties, you can use type methods to access data across all instances. You call type methods on the type itself, instead of on an instance. To define a type method, you prefix it with the static modifier.

struct Math {
  // 1
  static func factorial(of number: Int) -> Int {
    // 2
    return (1...number).reduce(1, *)
  }
}

extensions

Key points

• Methods are behaviors that extend the functionality of a type.
• A method is a function defined inside of a named type.
• A method can access the value of an instance by using the keyword self.
• Initializers are methods that aid in the creation of a new instance.