Builder.swift

import Foundation

@dynamicMemberLookup
public struct Builder<Base: AnyObject> {

    let _build: () -> Base

    public init(_ build: @escaping () -> Base) {
        self._build = build
    }

    public init(_ base: Base) {
        self._build = { base }
    }

    public subscript<Value>(dynamicMember keyPath: ReferenceWritableKeyPath<Base, Value>) -> (Value) -> Builder<Base> {
        { [build = _build] value in
            Builder {
                let object = build()
                object[keyPath: keyPath] = value
                return object
            }
        }
    }

    public func build() -> Base {
        _build()
    }

    public func set<Value>(_ keyPath: ReferenceWritableKeyPath<Base, Value>, to value: Value) -> Builder<Base> {
        Builder {
            let object = build()
            object[keyPath: keyPath] = value
            return object
        }
    }

    public func `do`(_ handler: @escaping (Base) -> Void) -> Builder<Base> {
        Builder { [build = _build] in
            let object = build()
            handler(object)
            return object
        }
    }
}

public protocol Buildable {
    associatedtype Base: AnyObject
    var builder: Builder<Base> { get }
}

public extension Buildable where Self: AnyObject {
    var builder: Builder<Self> {
        Builder(self)
    }
}

extension NSObject: Buildable {}

https://gist.github.com/JeanVinge/18489ba5f61620e886d2375cbd448f55 오리지날?