如何在 Swift 中打印变量的类型或类? [英] How do I print the type or class of a variable in Swift?

问题描述

有没有办法在 swift 中打印变量的运行时类型?例如:

Is there a way to print the runtime type of a variable in swift? For example:

var now = NSDate()
var soon = now.dateByAddingTimeInterval(5.0)

println("\(now.dynamicType)") 
// Prints "(Metatype)"

println("\(now.dynamicType.description()")
// Prints "__NSDate" since objective-c Class objects have a "description" selector

println("\(soon.dynamicType.description()")
// Compile-time error since ImplicitlyUnwrappedOptional<NSDate> has no "description" method

在上面的示例中，我正在寻找一种方法来表明变量soon"的类型为 ImplicitlyUnwrappedOptional，或者至少是 NSDate!.

In the example above, I'm looking for a way to show that the variable "soon" is of type ImplicitlyUnwrappedOptional<NSDate>, or at least NSDate!.

推荐答案

2016 年 9 月更新

Swift 3.0:使用 type(of:)，例如type(of: someThing)(因为删除了 dynamicType 关键字)

Swift 3.0: Use type(of:), e.g. type(of: someThing) (since the dynamicType keyword has been removed)

2015 年 10 月更新:

我将下面的示例更新为新的 Swift 2.0 语法(例如，println 被替换为 print，toString() 现在是 String()).

I updated the examples below to the new Swift 2.0 syntax (e.g. println was replaced with print, toString() is now String()).

来自 Xcode 6.3 发行说明:

@nschum 在评论中指出 Xcode6.3 发行说明 展示另一种方式:

@nschum points out in the comments that the Xcode 6.3 release notes show another way:

类型值现在在与println 或字符串插值.

Type values now print as the full demangled type name when used with println or string interpolation.

import Foundation

class PureSwiftClass { }

var myvar0 = NSString() // Objective-C class
var myvar1 = PureSwiftClass()
var myvar2 = 42
var myvar3 = "Hans"

print( "String(myvar0.dynamicType) -> \(myvar0.dynamicType)")
print( "String(myvar1.dynamicType) -> \(myvar1.dynamicType)")
print( "String(myvar2.dynamicType) -> \(myvar2.dynamicType)")
print( "String(myvar3.dynamicType) -> \(myvar3.dynamicType)")

print( "String(Int.self)           -> \(Int.self)")
print( "String((Int?).self         -> \((Int?).self)")
print( "String(NSString.self)      -> \(NSString.self)")
print( "String(Array<String>.self) -> \(Array<String>.self)")

输出:

String(myvar0.dynamicType) -> __NSCFConstantString
String(myvar1.dynamicType) -> PureSwiftClass
String(myvar2.dynamicType) -> Int
String(myvar3.dynamicType) -> String
String(Int.self)           -> Int
String((Int?).self         -> Optional<Int>
String(NSString.self)      -> NSString
String(Array<String>.self) -> Array<String>

Xcode 6.3 更新:

您可以使用_stdlib_getDemangledTypeName():

print( "TypeName0 = \(_stdlib_getDemangledTypeName(myvar0))")
print( "TypeName1 = \(_stdlib_getDemangledTypeName(myvar1))")
print( "TypeName2 = \(_stdlib_getDemangledTypeName(myvar2))")
print( "TypeName3 = \(_stdlib_getDemangledTypeName(myvar3))")

并将其作为输出:

TypeName0 = NSString
TypeName1 = __lldb_expr_26.PureSwiftClass
TypeName2 = Swift.Int
TypeName3 = Swift.String

原答案:

在 Xcode 6.3 之前 _stdlib_getTypeName 获得了变量的重整类型名称.Ewan Swick 的博客条目 有助于破译这些字符串:

Prior to Xcode 6.3 _stdlib_getTypeName got the mangled type name of a variable. Ewan Swick's blog entry helps to decipher these strings:

例如_TtSi 代表 Swift 内部的 Int 类型.

e.g. _TtSi stands for Swift's internal Int type.

Mike Ash 有一个很棒的博客涵盖同一主题的条目.

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