Golang 設計模式系列4: 適配器模式（Adapter design pattern）

適配器模式(Adapter Pattern) ：將一個接口轉換成客戶希望的另一個接口，適配器模式使接口不兼容的那些類可以一起工作，其別名爲包裝器(Wrapper)。適配器模式既可以作爲類結構型模式，也可以作爲對象結構型模式。

適配器模式包含如下角色：

Target：目標抽象類
Adapter：適配器類
Adaptee：適配者類
Client：客戶類

實現

1. Target：目標抽象類

type LegacyPrinter interface {
	Print(s string) string
}

2. Adaptee：適配者類

type MyLegacyPrinter struct{}

func (l *MyLegacyPrinter) Print(s string) (newMsg string) {
	newMsg = fmt.Sprintf("Legacy Printer: %s\n", s)
	println(newMsg)
	return
}

3. Client：客戶類

type ModernPrinter interface {
	PrintStored() string
}

4. Adapter：適配器類

type PrinterAdapter struct {
	OldPrinter LegacyPrinter
	Msg        string
}

func (p *PrinterAdapter) PrintStored() (newMsg string) {
	if p.OldPrinter != nil {
		newMsg = fmt.Sprintf("Adapter: %s", p.Msg)
		newMsg = p.OldPrinter.Print(newMsg)
	} else {
		newMsg = p.Msg
	}
	return
}

測試

func TestAdapter(t *testing.T) {
	msg := "Hello World!"
	adapter := PrinterAdapter{OldPrinter: &MyLegacyPrinter{}, Msg: msg}
	returnedMsg := adapter.PrintStored()
	if returnedMsg != "Legacy Printer: Adapter: Hello World!\n" {
		t.Errorf("Message didn't match: %s\n", returnedMsg)
	}
	adapter = PrinterAdapter{OldPrinter: nil, Msg: msg}
	returnedMsg = adapter.PrintStored()
	if returnedMsg != "Hello World!" {
		t.Errorf("Message didn't match: %s\n", returnedMsg)
	}
}

測試結果：

=== RUN   TestAdapter
Legacy Printer: Adapter: Hello World!

--- PASS: TestAdapter (0.00s)
PASS