add decorator

Author: senghoo

20_decorator/README.md

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+# 装饰模式
+
+装饰模式使用对象组合的方式动态改变或增加对象行为。
+
+Go语言借助于匿名组合和非入侵式接口可以很方便实现装饰模式。
+
+使用匿名组合，在装饰器中不必显式定义转调原对象方法。

20_decorator/decorator.go

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+package decorator
+
+type Component interface {
+	Calc() int
+}
+
+type ConcreteComponent struct{}
+
+func (*ConcreteComponent) Calc() int {
+	return 0
+}
+
+type MulDecorator struct {
+	Component
+	num int
+}
+
+func WarpMulDecorator(c Component, num int) Component {
+	return &MulDecorator{
+		Component: c,
+		num:       num,
+	}
+}
+
+func (d *MulDecorator) Calc() int {
+	return d.Component.Calc() * d.num
+}
+
+type AddDecorator struct {
+	Component
+	num int
+}
+
+func WarpAddDecorator(c Component, num int) Component {
+	return &AddDecorator{
+		Component: c,
+		num:       num,
+	}
+}
+
+func (d *AddDecorator) Calc() int {
+	return d.Component.Calc() + d.num
+}

20_decorator/decorator_test.go

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+package decorator
+
+import "fmt"
+
+func ExampleDecorator() {
+	var c Component = &ConcreteComponent{}
+	c = WarpAddDecorator(c, 10)
+	c = WarpMulDecorator(c, 8)
+	res := c.Calc()
+
+	fmt.Printf("res %d\n", res)
+	// Output:
+	// res 80
+}