如何在 Swift 中确定变量的类型 [英] How to determine the type of a variable in Swift

问题描述

Swift 中是否有确定变量类型的函数?我认为 Python 中可能有类似 type() 之类的东西.

Is there a function to determine the variable type in Swift? I presume there might be something like like type() in Python.

我想要一种方法来判断一个变量是 Swift 中的 Foundation 对象还是 C 变量.像 NSString 与字符串，或 NSArray 与数组.这样我就可以在控制台中注销它并清楚地看到它是什么.

I'd like a way to judge if a variable is a Foundation object or C variable in Swift. Like NSString vs String, or NSArray vs array. So that I can log it out in console and see clearly what it is.

例如，我想知道为下面的第一个 array 推断的类型:

For example, I would like to know the type inferred for the the first array below:

var array = [1,2,3]  // by default NSArray or array?
var array:[Int] = [1,2,3]
var array:NSArray = [1,2,3]
var array:Array<Any> = [1,2,3]

我在 这个问题，但我会说这与我想问的完全不同.

I have seen answers for judging if a given variable is a kind of given type in this question, but I'll say it's quite different from what I want to ask.

推荐答案

您可以使用 .dynamicType 属性获取对值的类型对象的引用.这相当于 Python 的 type() 函数，并在 在语言参考下的 Swift 文档:类型:元类型类型.

You can get a reference to the type object of a value by using the .dynamicType property. This is equivalent to Python's type() function, and is mentioned in the Swift documentation under Language Reference: Types: Metatype Type.

var intArray = [1, 2, 3]
let typeOfArray = intArray.dynamicType

使用这个类型对象，我们可以创建一个相同数组类型的新实例.

With this type object, we are able to create a new instance of the same array type.

var newArray = typeOfArray()
newArray.append(5)
newArray.append(6)
println(newArray)

[5, 6]

通过尝试附加一个浮点数，我们可以看到这个新值是相同的类型([Int]):

We can see that this new value is of the same type ([Int]) by attempting to append a float:

newArray.append(1.5)

error: type 'Int' does not conform to protocol 'FloatLiteralConvertible'

如果我们导入 Cocoa 并使用混合类型的数组字面量，我们可以看到创建了一个 NSArray:

If we import Cocoa and use an array literal with mixed types, we can see that an NSArray is created:

import Cocoa

var mixedArray = [1, "2"]
let mixedArrayType = mixedArray.dynamicType

var newArray = mixedArrayType()
var mutableArray = newArray.mutableCopy() as NSMutableArray

mutableArray.addObject(1)
mutableArray.addObject(1.5)
mutableArray.addObject("2")

println(mutableArray)

(1, "1.5", 2)

但是，此时似乎没有任何通用方法来生成类型对象的字符串描述，因此这可能无法起到您所询问的调试作用.

However, at this point there does not seem to be any general way to generate a string description of a type object, so this may not serve the debugging role that you were asking about.

从 NSObject 派生的类型确实有一个 .description() 方法，正如使用的 在 SiLo 的回答中，

Types derived from NSObject do have a .description() method, as is used in SiLo's answer,

println(mixedArrayType.description())

__NSArrayI

然而，这并不存在于诸如 Swift 的内置数组之类的类型上.

However this is not present on types such as Swift's built-in arrays.

println(typeOfArray.description())

error: '[Int].Type' does not have a member named 'description'

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