golang不到30行代码实现依赖注入的方法

package di

import (
 "sync"
 "reflect"
 "fmt"
 "strings"
 "errors"
)

var (
 ErrFactoryNotFound = errors.New("factory not found")
)

type factory = func() (interface{}, error)
// 容器
type Container struct {
 sync.Mutex
 singletons map[string]interface{}
 factories map[string]factory
}
// 容器实例化
func NewContainer() *Container {
 return &Container{
  singletons: make(map[string]interface{}),
  factories: make(map[string]factory),
 }
}

// 注册单例对象
func (p *Container) SetSingleton(name string, singleton interface{}) {
 p.Lock()
 p.singletons[name] = singleton
 p.Unlock()
}

// 获取单例对象
func (p *Container) GetSingleton(name string) interface{} {
 return p.singletons[name]
}

// 获取实例对象
func (p *Container) GetPrototype(name string) (interface{}, error) {
 factory, ok := p.factories[name]
 if !ok {
  return nil, ErrFactoryNotFound
 }
 return factory()
}

// 设置实例对象工厂
func (p *Container) SetPrototype(name string, factory factory) {
 p.Lock()
 p.factories[name] = factory
 p.Unlock()
}

// 注入依赖
func (p *Container) Ensure(instance interface{}) error {
 elemType := reflect.TypeOf(instance).Elem()
 ele := reflect.ValueOf(instance).Elem()
 for i := 0; i < elemType.NumField(); i++ { // 遍历字段
  fieldType := elemType.Field(i)
  tag := fieldType.Tag.Get("di") // 获取tag
  diName := p.injectName(tag)
  if diName == "" {
   continue
  }
  var (
   diInstance interface{}
   err  error
  )
  if p.isSingleton(tag) {
   diInstance = p.GetSingleton(diName)
  }
  if p.isPrototype(tag) {
   diInstance, err = p.GetPrototype(diName)
  }
  if err != nil {
   return err
  }
  if diInstance == nil {
   return errors.New(diName + " dependency not found")
  }
  ele.Field(i).Set(reflect.ValueOf(diInstance))
 }
 return nil
}

// 获取需要注入的依赖名称
func (p *Container) injectName(tag string) string {
 tags := strings.Split(tag, ",")
 if len(tags) == 0 {
  return ""
 }
 return tags[0]
}

// 检测是否单例依赖
func (p *Container) isSingleton(tag string) bool {
 tags := strings.Split(tag, ",")
 for _, name := range tags {
  if name == "prototype" {
   return false
  }
 }
 return true
}

// 检测是否实例依赖
func (p *Container) isPrototype(tag string) bool {
 tags := strings.Split(tag, ",")
 for _, name := range tags {
  if name == "prototype" {
   return true
  }
 }
 return false
}

// 打印容器内部实例
func (p *Container) String() string {
 lines := make([]string, 0, len(p.singletons)+len(p.factories)+2)
 lines = append(lines, "singletons:")
 for name, item := range p.singletons {
  line := fmt.Sprintf(" %s: %x %s", name, &item, reflect.TypeOf(item).String())
  lines = append(lines, line)
 }
 lines = append(lines, "factories:")
 for name, item := range p.factories {
  line := fmt.Sprintf(" %s: %x %s", name, &item, reflect.TypeOf(item).String())
  lines = append(lines, line)
 }
 return strings.Join(lines, "\n")
}

package main

import (
 "di"
 "database/sql"
 "fmt"
 "os"
 _ "github.com/go-sql-driver/mysql"
 "demo"
)

func main() {
 container := di.NewContainer()
 db, err := sql.Open("mysql", "root:root@tcp(localhost)/sampledb")
 if err != nil {
  fmt.Printf("error: %s\n", err.Error())
  os.Exit(1)
 }
 container.SetSingleton("db", db)
 container.SetPrototype("b", func() (interface{}, error) {
  return demo.NewB(), nil
 })

 a := demo.NewA()
 if err := container.Ensure(a); err != nil {
  fmt.Println(err)
  return
 }
 // 打印指针，确保单例和实例的指针地址
 fmt.Printf("db: %p\ndb1: %p\nb: %p\nb1: %p\n", a.Db, a.Db1, &a.B, &a.B1)
}