图案装饰器

Decorator模式是指结构设计模式。

装饰器用作继承的替代方法来扩展类的功能。
有一项任务是根据产品类型扩展应用程序的功能。客户需要三种类型的产品——基础、专业、终极。
基本的–统计字符数，专业–功能基本+以大写字母打印文本，终极＆#8211;基本+专业+打印文字“ULTIMATE”。
我们使用继承来实现它：

protocol Feature {
	func textOperation(text: String)
}

class BasicVersionFeature: Feature {
	func textOperation(text: String) {
		print("\(text.count)")
	}
}

class ProfessionalVersionFeature: BasicVersionFeature {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("\(text.uppercased())")
	}
}

class UltimateVersionFeature: ProfessionalVersionFeature {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("ULTIMATE: \(text)")
	}
}

let textToFormat = "Hello Decorator"

let basicProduct = BasicVersionFeature()
basicProduct.textOperation(text: textToFormat)

let professionalProduct = ProfessionalVersionFeature()
professionalProduct.textOperation(text: textToFormat)

let ultimateProduct = UltimateVersionFeature()
ultimateProduct.textOperation(text: textToFormat)

现在有需求实现“极致之光”产品——基本版 + 旗舰版，但没有专业版的功能。第一个发生是因为……您必须为这样一个简单的任务创建一个单独的类并复制代码。
让我们继续使用继承来实现：

protocol Feature {
	func textOperation(text: String)
}

class BasicVersionFeature: Feature {
	func textOperation(text: String) {
		print("\(text.count)")
	}
}

class ProfessionalVersionFeature: BasicVersionFeature {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("\(text.uppercased())")
	}
}

class UltimateVersionFeature: ProfessionalVersionFeature {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("ULTIMATE: \(text)")
	}
}

class UltimateLightVersionFeature: BasicVersionFeature {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("ULTIMATE: \(text)")	
	}
}

let textToFormat = "Hello Decorator"

let basicProduct = BasicVersionFeature()
basicProduct.textOperation(text: textToFormat)

let professionalProduct = ProfessionalVersionFeature()
professionalProduct.textOperation(text: textToFormat)

let ultimateProduct = UltimateVersionFeature()
ultimateProduct.textOperation(text: textToFormat)

let ultimateLightProduct = UltimateLightVersionFeature()
ultimateLightProduct.textOperation(text: textToFormat)

为了清楚起见，可以进一步开发该示例，但即使现在，支持基于继承基础的系统的复杂性也是可见的——麻烦且缺乏灵活性。
装饰器是一组描述功能的协议，是一个抽象类，其中包含对扩展功能的装饰器类的子具体实例的引用。
让我们使用以下模式重写上面的示例：

protocol Feature {
	func textOperation(text: String)
}

class FeatureDecorator: Feature {
	private var feature: Feature?
	
	init(feature: Feature? = nil) {
		self.feature = feature
	}
	
	func textOperation(text: String) {
		feature?.textOperation(text: text)
	}
}

class BasicVersionFeature: FeatureDecorator {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("\(text.count)")
	}
}

class ProfessionalVersionFeature: FeatureDecorator {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("\(text.uppercased())")
	}
}

class UltimateVersionFeature: FeatureDecorator {
	override func textOperation(text: String) {
		super.textOperation(text: text)
		print("ULTIMATE: \(text)")
	}
}

let textToFormat = "Hello Decorator"

let basicProduct = BasicVersionFeature(feature: UltimateVersionFeature())
basicProduct.textOperation(text: textToFormat)

let professionalProduct = ProfessionalVersionFeature(feature: UltimateVersionFeature())
professionalProduct.textOperation(text: textToFormat)

let ultimateProduct = BasicVersionFeature(feature: UltimateVersionFeature(feature: ProfessionalVersionFeature()))
ultimateProduct.textOperation(text: textToFormat)

let ultimateLightProduct = BasicVersionFeature(feature: UltimateVersionFeature())
ultimateLightProduct.textOperation(text: textToFormat)

现在我们可以创建任何类型产品的变体——在应用程序启动阶段初始化组合类型就足够了，下面的例子是Ultimate + Professional版本的创建：

ultimateProfessionalProduct.textOperation(text: textToFormat)

来源

https://refactoring.guru/ru/design-patterns/decorator

源代码

https://gitlab.com/demensdeum/patterns

图案装饰器

来源

源代码

Published by demensdeum

Leave a Comment