sort by keypath

SortByKeyPath.swift

extension Collection {
    func sorted<Value: Comparable>(on property: KeyPath<Element, Value>, by areInIncreasingOrder: (Value, Value) -> Bool) -> [Element] {
        return sorted { currentElement, nextElement in
            areInIncreasingOrder(currentElement[keyPath: property], nextElement[keyPath: property])
        }
    }
}

extension MutableCollection where Self: RandomAccessCollection {
    mutating func sort<Value: Comparable>(on property: KeyPath<Element, Value>, by order: (Value, Value) throws -> Bool) rethrows {
        try sort {  try order($0[keyPath: property], $1[keyPath: property]) }
    }
}

struct User {
    private(set) var name: String
    private(set) var age: Int
}

var users = [User(name: "Aaina", age: 10), User(name: "Tia", age: 20), User(name: "Ria", age: 5)]

users.sort(on: \User.age, by: <)
let names = users.map(\.age)
print(names)
// Prints [5, 10, 20]