swift 有一个特别的关键字 – extension
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| extension Double{
var km: Double { return self * 1_000.0 }
var m: Double { return self }
var cm: Double { return self / 100.0 }
var mm: Double { return self / 1_000.0 }
var ft: Double { return self / 3.28084 }
}
let oneInch = 25.4.mm
println("One inch is \(oneInch) meters")
let aMarathon = 42.km + 195.m
println("Amarathon is \(aMarathon) meters long")
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马上想到的是 ruby monkey-patch
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| class Fixnum
def seconds
return self
end
def minutes
return self*60
end
def days
return self*60*60
end
end
5.seconds
2.minutes
1.days
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在ios的例子中 ViewControllerExtensions 扩展ViewController, 继承 UITableViewDataSource , 并实现 protocol ,
类似ruby中用 module 扩展class.
参考
Swift扩展-Extension