Withable

withable.swift

struct Person {
    var firstName, lastName: String
}

let john = Person(firstName: "John", lastName: "Doe")

protocol Withable {

    func with(changes: (inout Self) -> Void) -> Self
    
}

extension Withable {
    
    func with(changes: (inout Self) -> Void) -> Self {
        var this = self
        changes(&this)
        return this
    }

}

extension Person: Withable {}


let carol = john.with {
    $0.firstName = "Carol"
}

print(carol)