/// Prototype Design Pattern
///
/// Intent: Lets you copy existing objects without making your code dependent on
/// their classes.
import XCTest
/// Swift has built-in cloning support. To add cloning support to your class,
/// you need to implement the NSCopying protocol in that class and provide the
/// implementation for the `copy` method.
class BaseClass: NSCopying, Equatable {
private var intValue = 1
private var stringValue = "Value"
required init(intValue: Int = 1, stringValue: String = "Value") {
self.intValue = intValue
self.stringValue = stringValue
}
/// MARK: - NSCopying
func copy(with zone: NSZone? = nil) -> Any {
let prototype = type(of: self).init()
prototype.intValue = intValue
prototype.stringValue = stringValue
print("Values defined in BaseClass have been cloned!")
return prototype
}
/// MARK: - Equatable
static func == (lhs: BaseClass, rhs: BaseClass) -> Bool {
return lhs.intValue == rhs.intValue && lhs.stringValue == rhs.stringValue
}
}
/// Subclasses can override the base `copy` method to copy their own data into
/// the resulting object. But you should always call the base method first.
class SubClass: BaseClass {
private var boolValue = true
func copy() -> Any {
return copy(with: nil)
}
override func copy(with zone: NSZone?) -> Any {
guard let prototype = super.copy(with: zone) as? SubClass else {
return SubClass() // oops
}
prototype.boolValue = boolValue
print("Values defined in SubClass have been cloned!")
return prototype
}
}
/// The client code.
class Client {
// ...
static func someClientCode() {
let original = SubClass(intValue: 2, stringValue: "Value2")
guard let copy = original.copy() as? SubClass else {
XCTAssert(false)
return
}
/// See implementation of `Equatable` protocol for more details.
XCTAssert(copy == original)
print("The original object is equal to the copied object!")
}
// ...
}
/// Let's see how it all works together.
class PrototypeConceptual: XCTestCase {
func testPrototype_NSCopying() {
Client.someClientCode()
}
}Values defined in BaseClass have been cloned!
Values defined in SubClass have been cloned!
The original object is equal to the copied object!