Swift with C example

SwiftC.swift

//original video https://realm.io/news/pragma-chris-eidhof-swift-c/
import Foundation

extension Comparable {
    static func compare (l: UnsafePointer<Void>, _ r: UnsafePointer<Void>) -> Int32 {
        let left: Self = UnsafePointer(l).memory
        let right: Self = UnsafePointer(r).memory
        
        if left < right { return -1 }
        if left == right { return 0 }
        return 1
    }
}

typealias CompareFunc = (UnsafePointer<Void>, UnsafePointer<Void>) -> Int32

func cmp(thunk: UnsafeMutablePointer<Void>, l: UnsafePointer<Void>, r: UnsafePointer<Void> ) -> Int32 {
    let compareFunc: CompareFunc = UnsafeMutablePointer(thunk).memory
    return compareFunc(l,r)
}

extension Array where Element: Comparable {
    func quicksort() -> [Element] {
        var array = self
        var compare = Element.compare
        qsort_r(&array, array.count, strideof(Element), &compare, cmp) 
        //here Chris recommends to use "strideof" instead of "sizeof" when working with C API. Because of different platform-specific bytes 
        return array
    }
    
    mutating func quicksortInline() {
        self = quicksort()
    }
    
}

var array = ["b", "A", "c", "A"]
array.quicksortInline()
print(array)