如何使集合类型约束中的泛型? [英] How to make generics in collection type constraint?
问题描述
我一直试图从字符串数组中提取非零值。如下所示。但是,我的资深人士希望它能够从其他类型中提取非零值。 我读过泛型可以帮助我处理不同的类型。我怎样才能使用泛型,以便我可以像使用扩展一样使用其他类型?
getNonNil
必须返回特定类型的提取的非零值(即 if array is [ String?]它必须返回[String],如果[Int?] 返回[Int])
因为我必须做进一步的计算。
我试过的是:
import Foundation
//扩展集合类型,使得collectiontype被限制为具有可选字符串的元素
extension CollectionType其中Self.Generator.Element ==可选< String> {
func getNonNil() - > [String] {
//过滤掉所有nil元素并强制使用map
打开它们返回self.filter({$ 0!= nil})。map({$ 0!})
}
}
//用法
让x:[String?] = [Er,Err,nil,errr]
x.getNonNil()。forEach {(str)in
print(str)
}
x.flatMap {$ 0}
//返回[Er,Err,errr],它是[String]
对于原始问题,通常您可以将协议引入可选类型(例如,通过 muukii / OptionalProtocol 包):
protocol OptionalProtocol {
associatedtype Wrapped
var value:Wrapped? {get}
}
扩展可选:OptionalProtocol {
public var value:Wrapped? {return self}
}
扩展名CollectionType其中Self.Generator.Element:OptionalProtocol {
func getNonNil() - > [Self.Generator.Element.Wrapped] {
...
}
}
I have been trying to extract non-nil values from the String array. Like below. But, my senior wants it to be able to extract non-nil values from other types too.
I read, generics could help me for handling different types. How can I use generics so that I get to use following like extension to work with other types too?
getNonNil
must return the extracted non-nil values of the specific type (i.e. if array is [String?] it must return [String], returns [Int] if [Int?])
Because I have to do further calculations.
What I have tried is below:
import Foundation
// Extended the collection-type so that collectiontype is constrained to having element with optional strings
extension CollectionType where Self.Generator.Element == Optional<String>{
func getNonNil() -> [String] {
// filter out all nil elements and forcefully unwrap them using map
return self.filter({$0 != nil}).map({$0!})
}
}
// Usage
let x: [String?] = ["Er", "Err", nil, "errr"]
x.getNonNil().forEach { (str) in
print(str)
}
For getNonNil
you could simply use
x.flatMap { $0 }
// returns ["Er", "Err", "errr"] which is [String]
For the original question, typically you could introduce a protocol to the Optional type (e.g. via the muukii/OptionalProtocol package):
protocol OptionalProtocol {
associatedtype Wrapped
var value: Wrapped? { get }
}
extension Optional: OptionalProtocol {
public var value: Wrapped? { return self }
}
extension CollectionType where Self.Generator.Element: OptionalProtocol {
func getNonNil() -> [Self.Generator.Element.Wrapped] {
...
}
}
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