Go语言中的装饰模式

Go 语言教程中的一个示例，用的装饰模式，实现了 Linux 的 cat 功能，还有一个 rot13 选项，可以对字符串进行简单加密。

实现了 reader 接口的 File 对象。

file.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package file

import (
	"os"
	"syscall"
)

type File struct {
	fd      int    // file descriptor number
	name    string // file name at Open time
}

func newFile(fd int, name string) *File {
	if fd < 0 {
		return nil
	}
	return &File{fd, name}
}

var (
	Stdin  = newFile(0, "/dev/stdin")
	Stdout = newFile(1, "/dev/stdout")
	Stderr = newFile(2, "/dev/stderr")
)

func Open(name string, mode int, perm int) (file *File, err os.Error) {
	r, e := syscall.Open(name, mode, perm)
	if e != 0 {
		err = os.Errno(e)
	}
	return newFile(r, name), err
}

func (file *File) Close() os.Error {
	if file == nil {
		return os.EINVAL
	}
	e := syscall.Close(file.fd)
	file.fd = -1  // so it can't be closed again
	if e != 0 {
		return os.Errno(e)
	}
	return nil
}

func (file *File) Read(b []byte) (ret int, err os.Error) {
	if file == nil {
		return -1, os.EINVAL
	}
	r, e := syscall.Read(file.fd, b)
	if e != 0 {
		err = os.Errno(e)
	}
	return int(r), err
}

func (file *File) Write(b []byte) (ret int, err os.Error) {
	if file == nil {
		return -1, os.EINVAL
	}
	r, e := syscall.Write(file.fd, b)
	if e != 0 {
		err = os.Errno(e)
	}
	return int(r), err
}

func (file *File) String() string {
	return file.name
}

 

reader 接口及装饰后的对象 rotate13，

cat_rot13.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
	"./file"
	"flag"
	"fmt"
	"os"
)

var rot13Flag = flag.Bool("rot13", false, "rot13 the input")

func rot13(b byte) byte {
	if 'a' <= b && b <= 'z' {
	   b = 'a' + ((b - 'a') + 13) % 26
	}
	if 'A' <= b && b <= 'Z' {
	   b = 'A' + ((b - 'A') + 13) % 26
	}
	return b
}

type reader interface {
	Read(b []byte) (ret int, err os.Error)
	String() string
}

type rotate13 struct {
	source	reader
}

func newRotate13(source reader) *rotate13 {
	return &rotate13{source}
}

func (r13 *rotate13) Read(b []byte) (ret int, err os.Error) {
	r, e := r13.source.Read(b)
	for i := 0; i < r; i++ {
		b[i] = rot13(b[i])
	}
	return r, e
}

func (r13 *rotate13) String() string {
	return r13.source.String()
}
// end of rotate13 implementation

func cat(r reader) {
	const NBUF = 512
	var buf [NBUF]byte

	if *rot13Flag {
		r = newRotate13(r)  // 用 rotate13 装饰 r，使得所有输出自动改变。
	}
	for {
		switch nr, er := r.Read(&buf); {
		case nr < 0:
			fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", r.String(), er.String())
			os.Exit(1)
		case nr == 0:  // EOF
			return
		case nr > 0:
			nw, ew := file.Stdout.Write(buf[0:nr])
			if nw != nr {
				fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", r.String(), ew.String())
			}
		}
	}
}

func main() {
	flag.Parse()   // Scans the arg list and sets up flags
	if flag.NArg() == 0 {
		cat(file.Stdin)
	}
	for i := 0; i < flag.NArg(); i++ {
		f, err := file.Open(flag.Arg(i), 0, 0)
		if f == nil {
			fmt.Fprintf(os.Stderr, "cat: can't open %s: error %s\n", flag.Arg(i), err)
			os.Exit(1)
		}
		cat(f)
		f.Close()
	}
}

 

有点长，但是用得很恰当，呵呵