什么是Swift相当于 – ？
在Objective-C中，可以在其类中添加一个description方法来帮助debugging：
@implementation MyClass - (NSString *)description { return [NSString stringWithFormat:@"<%@: %p, foo = %@>", [self class], foo _foo]; } @end
然后在debugging器中，你可以这样做：
po fooClass <MyClass: 0x12938004, foo = "bar">
Swift中的等价物是什么？ Swift的REPL输出可能会有所帮助：
1> class MyClass { let foo = 42 } 2> 3> let x = MyClass() x: MyClass = { foo = 42 }
但我想覆盖这个行为打印到控制台：
4> println("x = \(x)") x = C11lldb_expr_07MyClass (has 1 child)
有没有办法清理这个println输出？ 我见过Printable协议：
/// This protocol should be adopted by types that wish to customize their /// textual representation. This textual representation is used when objects /// are written to an `OutputStream`. protocol Printable { var description: String { get } }
我想这会自动被“看到” println但它似乎并不是这样的情况：
1> class MyClass: Printable { 2. let foo = 42 3. var description: String { get { return "MyClass, foo = \(foo)" } } 4. } 5> 6> let x = MyClass() x: MyClass = { foo = 42 } 7> println("x = \(x)") x = C11lldb_expr_07MyClass (has 1 child)
相反，我必须明确地调用description：
8> println("x = \(x.description)") x = MyClass, foo = 42
有没有更好的办法？
通过一些实验，我发现Printable和DebugPrintable协议在编译实际应用程序时工作，但不在REPL或Playground中。
注意 ：你写的代码是正确的，但在这种情况下，你可能正在寻找DebugPrintable
Swift已经将这些协议重命名为CustomStringConvertible和CustomDebugStringConvertible – 虽然编译器当前有帮助地告诉你它已经完成了:)
在Swift中使用CustomStringConvertible和CustomDebugStringConvertible协议的例子：
PageContentViewController.swift
import UIKit class PageContentViewController: UIViewController { var pageIndex : Int = 0 override var description : String { return "**** PageContentViewController\npageIndex equals \(pageIndex) ****\n" } override var debugDescription : String { return "---- PageContentViewController\npageIndex equals \(pageIndex) ----\n" } ... }
ViewController.swift
import UIKit class ViewController: UIViewController { /* Called after the controller's view is loaded into memory. */ override func viewDidLoad() { super.viewDidLoad() let myPageContentViewController = self.storyboard!.instantiateViewControllerWithIdentifier("A") as! PageContentViewController print(myPageContentViewController) print(myPageContentViewController.description) print(myPageContentViewController.debugDescription) } ... }
哪打印出来：
**** PageContentViewController pageIndex equals 0 **** **** PageContentViewController pageIndex equals 0 **** ---- PageContentViewController pageIndex equals 0 ----
注意：如果你有一个自定义类没有从UIKit或者基础库中包含的任何类inheritance，那么使它inheritanceNSObject类或者使它符合CustomStringConvertible和CustomDebugStringConvertible协议。
只需使用CustomStringConvertible和var description: String { return "Some string" }
适用于Xcode 7.0testing版
class MyClass: CustomStringConvertible { var string: String? var description: String { //return "MyClass \(string)" return "\(self.dynamicType)" } } var myClass = MyClass() // this line outputs MyClass nil // and of course print("\(myClass)") // Use this newer versions of Xcode var description: String { //return "MyClass \(string)" return "\(type(of: self))" }
有关CustomStringConvertible的答案是要走的路。 就个人而言，为了保持类（或结构）的定义尽可能的干净，我还要将描述代码分隔成一个单独的扩展：
class foo { // Just the basic foo class stuff. var bar = "Humbug!" } extension foo: CustomStringConvertible { var description: String { return bar } } let xmas = foo() print(xmas) // Prints "Humbug!"
class SomeBaseClass: CustomStringConvertible { //private var string: String = "SomeBaseClass" var description: String { return "\(self.dynamicType)" } // Use this in newer versions of Xcode var description: String { return "\(type(of: self))" } } class SomeSubClass: SomeBaseClass { // If needed one can override description here } var mySomeBaseClass = SomeBaseClass() // Outputs SomeBaseClass var mySomeSubClass = SomeSubClass() // Outputs SomeSubClass var myOtherBaseClass = SomeSubClass() // Outputs SomeSubClass
struct WorldPeace: CustomStringConvertible { let yearStart: Int let yearStop: Int var description: String { return "\(yearStart)-\(yearStop)" } } let wp = WorldPeace(yearStart: 2020, yearStop: 2040) print("world peace: \(wp)") // outputs: // world peace: 2020-2040
