go-patterns/creational/factory.md

Factory Method Pattern

Factory method creational design pattern allows creating objects without having to specify the exact type of the object that will be created.
工厂方法创建型设计模式允许创建对象，不用指定要创建对象的类型。

Implementation

The example implementation shows how to provide a data store with different backends such as in-memory, disk storage.
示例实现展示了如何使用不同的后端，如内存、磁盘存储。

Types(对象类型)

package data

import "io"

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

Different Implementations(不同实现)

package data

type StorageType int

// 类型实现对象枚举
const (
    DiskStorage StorageType = 1 << iota
    TempStorage
    MemoryStorage
)

// 工厂方法(实例化对象)
func NewStore(t StorageType) Store {
    switch t {
    case MemoryStorage:
        return newMemoryStorage( /*...*/ )
    case DiskStorage:
        return newDiskStorage( /*...*/ )
    default:
        return newTempStorage( /*...*/ )
    }
}

Usage

With the factory method, the user can specify the type of storage they want. 使用工厂方法，指定实现类型枚举。

// 给工厂方法提供实现类型枚举
s, _ := data.NewStore(data.MemoryStorage)
f, _ := s.Open("file")

n, _ := f.Write([]byte("data"))
defer f.Close()