Comparison between Binding and Endo when lifting by WritableKeyPath

ProfunctorWritableKeyPath.swift

import Foundation
import SwiftUI

// As pointed by @pointfreeco (no pun intended) here https://twitter.com/pointfreeco/status/1285209505714843648
// these types can't be called Profunctor as they are covariant and contravariant on the very same element (single
// generic parameter, instead of 2). That way, function "dimap" here is academically incorrect and either contramap
// or pullback should be used, instead.

struct Endo<Value> {
    let run: (Value) -> Value
    init(_ fn: @escaping (Value) -> Value) {
        self.run = fn
    }
}

// Lift profunctors using pair of functions in opposite direction
extension Binding {
    // pullback would be a better name, check comment on the top
    func dimap<NewValue>(getter getterMap: @escaping (Value) -> NewValue, setter setterContramap: @escaping (NewValue) -> Value) -> Binding<NewValue> {
        Binding<NewValue> {
            getterMap(self.wrappedValue)
        } set: {
            self.wrappedValue = setterContramap($0)
        }
    }
}

extension Endo {
    // pullback would be a better name, check comment on the top
    func dimap<NewValue>(output outputMap: @escaping (Value) -> NewValue, input inputContramap: @escaping (NewValue) -> Value) -> Endo<NewValue> {
        Endo<NewValue> { (input: NewValue) -> NewValue in
            outputMap(self.run(inputContramap(input)))
        }
    }
}

// Lift profunctors using WritableKeyPath
extension Binding {
    // pullback would be a better name, check comment on the top
    func dimap<NewValue>(_ keyPath: WritableKeyPath<Value, NewValue>) -> Binding<NewValue> {
        Binding<NewValue> {
            self.wrappedValue[keyPath: keyPath]
        } set: {
            self.wrappedValue[keyPath: keyPath] = $0
        }
    }
}

extension Endo {
    // pullback would be a better name, check comment on the top
    func dimap<NewValue>(_ keyPath: WritableKeyPath<NewValue, Value> /* contravariant WritableKeyPath */) -> Endo<NewValue> {
        Endo<NewValue> { newValue in
            var newValueMutable = newValue
            newValueMutable[keyPath: keyPath] = self.run(newValueMutable[keyPath: keyPath])
            return newValueMutable
        }
    }
}