Factory Method Pattern

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本文讨论了 Factory Method Pattern 工厂方法模式的 Go 实现

Factory Method Pattern 工厂方法

  • 有利于产品族内产品的增加。

接口类型

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package data

import "io"

type Store interface {
	Open(string) (io.ReadWriteCloser, error)
}

不同的产品实现

  • diskStorage : 磁盘存储实现
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package data

import (
	"io"
)

type diskStorage struct {
	Store
}

func newDiskStorage() (Store, error) {
	return new(diskStorage), nil
}

func (p *diskStorage) Open(f string) (rwc io.ReadWriteCloser, err error) {
        // ...
	return rwc, err
}
  • memoryStorage : 内存存储实现
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package data

import (
	"io"
)

type memory struct {
	io.ReadWriteCloser
	buf []byte
}

func (m *memory) Read(p []byte) (n int, err error) {
	for i, v := range m.buf {
		p[i] = v
	}
	return len(p), nil
}

func (m *memory) Write(p []byte) (n int, err error) {
	m.buf = append(m.buf, p...)
	return len(p), nil
}

func (m *memory) Close() error {
	m.buf = m.buf[0:0]
	return nil
}

type memoryStorage struct {
	Store
}

func newMemoryStorage() (Store, error) {
	return new(memoryStorage), nil
}

func (m *memoryStorage) Open(f string) (rwc io.ReadWriteCloser, err error) {
	return new(memory), nil
}
  • tempStorage
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package data

import "io"

type tempStorage struct {
	Store
}

func newTempStorage() (Store, error) {
	return new(tempStorage), nil
}

func (t *tempStorage) Open(f string) (rwc io.ReadWriteCloser, err error) {
	return rwc, err
}

工厂方法实现

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package data

type StorageType int

const (
	DiskStorage StorageType = 1 << iota
	TempStorage
	MemoryStorage
)

func NewStore(t StorageType) (s Store, err error) {
	switch t {
	case MemoryStorage:
		return newMemoryStorage()
	case DiskStorage:
		return newDiskStorage()
	default:
		return newTempStorage()
	}
}

使用

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func main() {
	store, _ := data.NewStore(data.MemoryStorage)
	f, _ := store.Open("file")
	defer f.Close()

	f.Write([]byte("Hello,"))
	f.Write([]byte(" factory method."))

	s := make([]byte, 100)
	n, _ := f.Read(s)

	fmt.Println(string(s[0:n]))
}