Swift中的Printable和DebugPrintable之间的区别 [英] Difference between Printable and DebugPrintable in Swift

问题描述

找到Swift等效的Cocoa description ，我在Swift中找到了以下协议： Printable 和 DebugPrintable 。

这两个协议有什么区别，我应该什么时候使用？

$ b $在XCode 6 Beta版本（版本6.2（6C101）），我发现println和debugPrintln使用描述if-and-only - 如果类从NSObject下降。我看不到或者使用debugDescription，但是在一个Playground中运行debugPrintln只输出到控制台，并不出现在操场本身。

  import Foundation 
 
 class Tdesc：NSObject，Printable，DebugPrintable {
 override var description：String {returnA description} 
 override var debugDescription： String {returnA debugDescription} 
} 
 
类Xdesc：Printable，DebugPrintable {
 var description：String {returnA description} 
 var debugDescription： String {returnA debugDescription} 
} 
 
 let t = Tdesc（）
 let x = Xdesc（）
 
 t.description 
 
 let z：String =x \（t）
 
 println（t）//在游乐场和控制台中显示描述
 
 debugPrintln（t）//在游乐场中不显示任何内容，但在控制台中的描述
 
 x.description 
 
 let y：String =x\ ）
 
 println（x）//在游乐场和控制台中显示__lldb_expr_405.Xdesc
 
 debugPrintln（x）
  

Looking for a Swift equivalent of Cocoa's description, I found the following protocols in Swift: Printable and DebugPrintable.

What's the difference between these two protocols and when should I use each one?

解决方案

In XCode 6 Beta (Version 6.2 (6C101)) I find that both println and debugPrintln use description if-and-only-if the class descends from NSObject. I don't see that either uses debugDescription at all but when run in a Playground debugPrintln outputs only to the Console and doesn't appear in the playground itself.

import Foundation

class Tdesc: NSObject, Printable, DebugPrintable {
    override var description: String {return "A description"}
    override var debugDescription: String {return "A debugDescription"}
}

class Xdesc: Printable, DebugPrintable {
    var description: String {return "A description"}
    var debugDescription: String {return "A debugDescription"}
}

let t = Tdesc()
let x = Xdesc()

t.description

let z: String = "x\(t)"

println(t)      // Displays "A description" in the Playground and Console

debugPrintln(t) // Displays nothing in the Playground but "A description" in the Console

x.description

let y: String = "x\(x)"

println(x)      // Displays "__lldb_expr_405.Xdesc" in the Playground and Console

debugPrintln(x)

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