A Swift's parameter packs new feature example

swift-parameter_packs.swift

import Foundation

struct Query<Element> {
    let key: String
    let value: Element
    
    var filter: String {
        return "\(key)=\(String(describing: value))"
    }
}

//
// The parameter packs in action
//
func query<each Filter>(_ parameter: repeat Query<each Filter>) -> String {
    // For each parameter received, obtain the `filter` property value
    let filters = (repeat (each parameter).filter)
    
    // Let's iterate over tuple and cast the values to strings
    let mirror = Mirror(reflecting: filters)
    let filter = mirror.children
                            .map({ String(describing: $0.value) })
                            .joined(separator: "&")
    
    return filter
}

// MARK: - Make some tests

let apiKey = Query(key: "api_key", value: "fasd_esp_00197500")
let currentPage = Query(key: "page", value: 1)
let offset = Query(key: "offset", value: 100)
let adultContent = Query(key: "includes_adult_content", value: false)

let firstQueryFilter = query(apiKey, offset, adultContent)
print(firstQueryFilter)

let nextQueryFilter = query(apiKey, currentPage, offset, adultContent)
print(nextQueryFilter)