Lens with @dynamicMemberLookup in Swift5.1

Lens.swift

import Foundation


struct Lens<Whole, Part> {
    let view: (Whole) -> Part
    let set: (Part, Whole) -> Whole
}

protocol LensCompatible {}

@dynamicMemberLookup
struct LensProxy<Base: LensCompatible> {
    subscript<T>(dynamicMember keyPath: WritableKeyPath<Base, T>) -> Lens<Base, T> {
        Lens<Base, T>(
            view: { $0[keyPath: keyPath] },
            set: { part, whole in
                var copy = whole
                copy[keyPath: keyPath] = part
                return copy
            })
    }
}

extension LensCompatible {
    static var lens: LensProxy<Self> {
        return LensProxy()
    }
}

// Apply

struct Location {
    var name: String
}
extension Location: LensCompatible {}
let locationNameLens = Location.lens.name // Lens<Location, String>