[Any]和contains（）的数组

问题描述

我正在尝试测试类型 [Any] 的数组是否包含特定类型的值（例如， Int ）。

I'm trying to test if an array of type [Any] contains a value of a specific type (say, Int).

我知道Swift不知道如何比较 Int 和值的类型，我想这就是自动完成模板中要表达的内容：

I'm aware that Swift does not know how to compare an Int and a value of arbitrary type, and I guess that's what's being expressed in the autocomplete template:

包含（谓词：（protocol<>））抛出- >布尔）

所以我尝试了以下代码：

So I tried this code:

let intValue:Int = 5 // for example

let isContained = myArrayOfAny.contains({ element in 
    return ((element as? Int) == intValue)
})

...并且可以编译（无法确定是否可以正常使用） ）;但仍然不能成为谓词（（协议））部分的首尾。这是什么意思？ SequenceType 的文档非常隐秘：

...and it compiles (can't make sure it works yet); but still can't make heads or tails of the predicate: (protocol<>) part. What does it mean? The documentation for SequenceType is quite cryptic:

contains(_: (Self.Generator.Element) throws -> Bool) rethrows -> Bool
 Default Implementation
Return true iff an element in self satisfies predicate.

Declaration
@warn_unused_result func contains(@noescape _ predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Bool

---

编辑：我很困惑，因为我看到的所有搜索结果都具有 Array 的 contains（）方法取要测试是否包含的值，例如：

---

I'm quite confused because, all search results I've seen have the contains() method of Array as just taking the value to be tested for containment, e.g.:

if myArrayOfInt.contains(someInt){
    ...

而不是闭包。

推荐答案

有两种不同的 contains（）方法（这两种协议的
扩展都是 SequenceType ）。第一个是

There are two different contains() methods (both protocolextensions to SequenceType). The first one is

extension SequenceType where Generator.Element : Equatable {
    /// Return `true` iff `element` is in `self`.
    @warn_unused_result
    public func contains(element: Self.Generator.Element) -> Bool
}

，它要求序列元素符合平等的
协议，该协议保证可以将它们与 == 进行比较：

and it requires that the sequence elements conform to the Equatableprotocol, which guarantees that they can be compared with ==:

public protocol Equatable {
    // ...
    public func ==(lhs: Self, rhs: Self) -> Bool
}

例如，在

let intValue:Int = 5
let myArrayOfInt = [4, 5, 6]
let isContained = myArrayOfInt.contains(intValue)

您有一个 Int 和<$ c $的数组c> Int 符合 Equatable ，
，因此此 contains（）方法可以用来检查某个元素的存在
。

you have an array of Int, and Int conforms to Equatable,so this contains() method can be used to check for the presenceof a certain element.

这不适用于

let myArrayOfAny : [Any] = [4, 5, 6]

因为任何不符合 Equatable 。在这里，您可以使用
作为第二个 contains（）方法

because Any does not conform to Equatable. Here you can usethe second contains() method

extension SequenceType {
    /// Return `true` iff an element in `self` satisfies `predicate`.
    @warn_unused_result
    public func contains(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Bool
}

需要一个谓词，即布尔值功能。将谓词应用于每个数组元素，而不是将
与 == 进行比较。
此方法不需要数组元素 Equatable 。

which takes a predicate, i.e. a boolean function. Instead of comparing with ==, the predicate is applied to each array element.This method does not require that the array elements are Equatable.

这就是您要做的

let myArrayOfAny : [Any] = [4, 5, 6]
let intValue:Int = 5 // for example
let isContained = myArrayOfAny.contains({ element in 
    return ((element as? Int) == intValue)
})

如果可以将任何数组元素转换为 Int，这将产生 true
并等于给定的 intValue 。

This will yield true if any array element can be cast to an Intand is equal to the given intValue.

可能会看到第一种方法使用频率更高，但是第二种
则更为通用，例如，如果myArrayOfCustomObjects.contains（{$ 0。$

The might see the first method more frequently but the secondis far more general, e.g.

if myArrayOfCustomObjects.contains ({ $0.someProperty == "foo" })

或

if myArrayOfInts.contains ({ $0 > 17 })

因此，第一个 contains（）是第二种的一种专门化形式，用于对平等的元素。它可以 实现为

So the first contains() is a kind of specialization of the second one for a simple containment check in arrays of equatable elements. It could be implemented as

extension SequenceType where Generator.Element : Equatable {

    public func contains(element: Self.Generator.Element) -> Bool {
        return self.contains({ $0 == element } )
    }
}

您会发现与 indexOf（）相同，它也有
两种风格：

You'll find the same with indexOf() which also comes intwo flavors:

extension CollectionType where Generator.Element : Equatable {
    // ...
    public func indexOf(element: Self.Generator.Element) -> Self.Index?
}

extension CollectionType {
    // ...
    public func indexOf(@noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Index?
}

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