如何检查一个元素是否在数组中 [英] How to check if an element is in an array

问题描述

在 Swift 中，如何检查一个元素是否存在于数组中?Xcode 没有关于 contain、include 或 has 的任何建议，快速搜索这本书一无所获.知道如何检查吗?我知道有一个方法 find 可以返回索引号，但是有没有一个方法可以返回一个布尔值，如 ruby​​ 的 #include??

In Swift, how can I check if an element exists in an array? Xcode does not have any suggestions for contain, include, or has, and a quick search through the book turned up nothing. Any idea how to check for this? I know that there is a method find that returns the index number, but is there a method that returns a boolean like ruby's #include??

我需要的示例:

var elements = [1,2,3,4,5]
if elements.contains(5) {
  //do something
}

推荐答案

Swift 2, 3, 4, 5:

let elements = [1, 2, 3, 4, 5]
if elements.contains(5) {
    print("yes")
}

contains() 是 SequenceType(用于 Equatable 元素的序列)而不是全局方法，如早期版本.

contains() is a protocol extension method of SequenceType (for sequences of Equatable elements) and not a global method as in earlier releases.

备注:

• 这个 contains() 方法要求序列元素采用 Equatable 协议，比较例如安德鲁斯的回答.
• 如果序列元素是 NSObject 子类的实例那么你必须覆盖 isEqual:，参见 Swift 中的 NSObject 子类:hash vs hashValue，isEqual vs ==.
• 还有另一种更通用的 contains() 方法，它不需要元素是相等的，而是将谓词作为论据，参见例如测试对象是否存在于Swift 的数组?.

• This contains() method requires that the sequence elements adopt the Equatable protocol, compare e.g. Andrews's answer.
• If the sequence elements are instances of a NSObject subclass then you have to override isEqual:, see NSObject subclass in Swift: hash vs hashValue, isEqual vs ==.
• There is another – more general – contains() method which does not require the elements to be equatable and takes a predicate as an argument, see e.g. Shorthand to test if an object exists in an array for Swift?.

Swift 旧版本:

let elements = [1,2,3,4,5]
if contains(elements, 5) {
    println("yes")
}

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