将通用免费函数转换为数组扩展 [英] Convert generic free function into Array extension

问题描述

我写了一些代码来执行游程编码和解码。我有我的编码函数作为Array的扩展方法，但我无法以类似的方式进行解码。这可能吗？

  func runLengthDecode< T：Equatable>（_ runLengthEncoding： [（element：T，count：Int）]） - > [T] {
 return runLengthEncoding.flatMap {repeatElement（$ 0.element，count：$ 0.count）} 
} 
  

我希望这个函数也是Array上的一个方法。一些行为：

 扩展数组< T>其中Element ==（元素：T，count：Int）{
 func runLengthDecode（） - > [T] {
 return self.flatMap {repeatElement（$ 0.element，count：$ 0.count）} 
} 
} 
   
 
解决方案
 
不是限制数组扩展，而是将约束移动到您的方法中：
 
 
 扩展数组{
 func runLengthDecode< T：Equatable>（） - > [T]其中Element ==（element：T，count：Int）{
 return flatMap {repeatElement（$ 0.element，count：$ 0.count）} 
} 
} 
  
或简单地 
 
 
 扩展数组{
 func runLengthDecode< T：Equatable>（） - > [T]其中Element ==（element：T，count：Int）{
 return flatMap（repeatElement）
} 
} 
  
 
I wrote some code to perform run length encoding and decoding. I have my encoding function as a method in an extension to Array, but I can't make the decoding in a similar fashion. Is this possible? I can't find any ways of introducing new generic types into extensions.
func runLengthDecode<T: Equatable>(_ runLengthEncoding: [(element: T, count: Int)]) -> [T] {
    return runLengthEncoding.flatMap{ repeatElement($0.element, count: $0.count)}
}
I wish this function were a method on Array, as well. Something along the lines of:
extension Array<T> where Element == (element: T, count: Int) {
    func runLengthDecode() -> [T] {
        return self.flatMap{ repeatElement($0.element, count: $0.count)}
    }
}

解决方案
Instead of constraining the array extension move the constraint to your method:
extension Array {
    func runLengthDecode<T: Equatable>() -> [T] where Element == (element: T, count: Int)  {
        return flatMap{ repeatElement($0.element, count: $0.count) }
    }
}
or simply
extension Array {
    func runLengthDecode<T: Equatable>() -> [T] where Element == (element: T, count: Int)  {
        return flatMap(repeatElement)
    }
}


                        
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