用自定义运算符覆盖类型转换 [英] Override typecasting with custom operators

问题描述

假设我有这样的事情：

var x: Int = 6
var y: Float = 11.5

结果必须写成这样

so, the result has to be written like this

var result = Float(x) * y

或

var result = x * Int(y)

这很有道理，对吧？然而，我认为这有点笨拙，所以我想为此做一些自定义操作符：

This makes sense, right ?
However, I think that a little clumsy, so I'm trying to make some custom operators for this:

infix operator *~ { associativity left precedence 150 } //floating

func *~ (lhs: Float, rhs: Int) -> Float {
    return lhs * Float(rhs)
}

func *~ (lhs: Int, rhs: Float) -> Float {
    return rhs * Float(lhs)
}


infix operator *| { associativity left precedence 150 } //Integer

func *| (lhs: Float, rhs: Int) -> Int {
    return Int(lhs) * rhs
}

func *| (lhs: Int, rhs: Float) -> Int {
    return Int(rhs) * lhs
}

其中有太多，所以我试图为这些功能做一个通用版本。我到目前为止的尝试：

It works but there are too many of them, so I'm trying to make a generic version for these functions. My attempt so far:

func *~ <T: FloatingPointType, V:IntegerType>(lhs: T, rhs: V) -> T {
    return lhs * T(rhs) 
    // error:
    // Could not find an overload for 'init' that accepts the supplied arguments
}

有人可以帮忙吗？谢谢。

Can somebody help please ? Thank you.

推荐答案

protocol Fraction {
    init(_ value: Double)
    var asDouble: Double { get }
}

extension Int     : Fraction { var asDouble : Double { return Double(self) } }
extension Double  : Fraction { var asDouble : Double { return self         } }
extension Float   : Fraction { var asDouble : Double { return Double(self) } }
extension CGFloat : Fraction { var asDouble : Double { return Double(self) } }

infix operator ** { associativity left precedence 170 }

func **(lhs:Int, rhs:Int) -> Int {
    return lhs * rhs
}
func **<T:Fraction, U:Fraction>(lhs:T, rhs:U) -> Double {
    return lhs.asDouble * rhs.asDouble

}

2 ** 2     // 4
2 ** 2.2   // 4.4
2.5 ** 2   //  5.0
2.2 ** 2.2 // 4.84

这篇关于用自定义运算符覆盖类型转换的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！