像NSObject一样获得描述

Question

如果您在Playgroud中运行以下内容

class Test {
  var description:String {
    return "This is Test"
  }
}

class Test1:NSObject {
  override var description:String {
    return "This is Test"
  }
}

let t = Test()
println(t)
let t1 = Test1()
println(t1)

你看到第一个println会输出一些调试器模糊,而第二个会输出内容description.

所以:是有办法,"正常"类将被视为相同的方式的子类NSObject,以便println将尊重的内容description属性？

Answer 1

从println()API文档:

/// Writes the textual representation of `object` and a newline character into
/// the standard output.
///
/// The textual representation is obtained from the `object` using its protocol
/// conformances, in the following order of preference: `Streamable`,
/// `Printable`, `DebugPrintable`.
///
/// Do not overload this function for your type.  Instead, adopt one of the
/// protocols mentioned above.
func println<T>(object: T)

因此,为了获得自定义println()表示,您的类必须(例如)Printable明确采用协议:

class Test : Printable {
    var description:String {
        return "This is Test"
    }
}

但是,这在Xcode 6.1.1的Playground中不起作用.它已在Xcode 6.3 beta中修复.从发行说明:

•在Playground中添加一致性现在可以按预期工作,...

我在API头文件中找不到这个,但似乎NSObject 已知(及其子类)符合Printable.因此,自定义说明适用于您的Test1班级.

在夫特2(Xcode中7),该Printable协议已经被重新命名为CustomStringConvertible:

class Test : CustomStringConvertible {
    public var description:String {
        return "This is Test"
    }
}

let t = Test()
print(t)
// This is Test