Builder.swift

@dynamicMemberLookup
struct Builder<Object> {
    let object: Object

    init(_ object: Object) {
        self.object = object
    }

    subscript<T>(dynamicMember keyPath: WritableKeyPath<Object, T>) -> (T) -> Builder<Object> {
        return {
            var copy = object
            copy[keyPath: keyPath] = $0
            return Builder(copy)
        }
    }

    func call(_ work: (Object) -> Void) -> Builder<Object> {
        work(object)
        return self
    }
}

usage.swift

// configure an existing object
let view1 = UIView()

Builder(view1)
    .backgroundColor(.white)
    .call { $0.addSubview(UIView()) }
    .isExclusiveTouch(true)


// create a new object
let view2 = Builder(UIView())
    .backgroundColor(.black)
    .object

The Setter type is required because we can't add @discardableResult to closures

very good