Golang如何用装饰器扩展对象功能

func loggingMiddleware(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        log.Printf("Received request: %s %s", r.Method, r.URL.Path)
        next(w, r)
    }
}

// 使用
http.HandleFunc("/hello", loggingMiddleware(func(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Hello, World!")
}))

type DataReader interface {
    Read() string
}

type FileReader struct{}

func (f *FileReader) Read() string {
    return "data from file"
}

type CachedReader struct {
    reader DataReader
    cache  string
    cached bool
}

func (c *CachedReader) Read() string {
    if !c.cached {
        c.cache = c.reader.Read()
        c.cached = true
        log.Println("Reading from source")
    } else {
        log.Println("Reading from cache")
    }
    return c.cache
}

reader := &CachedReader{reader: &FileReader{}}
fmt.Println(reader.Read()) // 第一次从源读取
fmt.Println(reader.Read()) // 第二次从缓存读取

type CompressedReader struct {
    reader DataReader
}

func (c *CompressedReader) Read() string {
    data := c.reader.Read()
    return "compressed(" + data + ")"
}

reader := &CompressedReader{
    reader: &CachedReader{
        reader: &FileReader{},
    },
}
fmt.Println(reader.Read())