go 依赖注入

在go语言中没有类以及构造函数的说法，只有类似的结构体：

package main

import "fmt"

type Books struct {
   title string
   author string
   subject string
   book_id int
}


func main() {

    // 创建一个新的结构体
    fmt.Println(Books{"Go 语言", "www.runoob.com", "Go 语言教程", 6495407})

    // 也可以使用 key => value 格式
    fmt.Println(Books{title: "Go 语言", author: "www.runoob.com", subject: "Go 语言教程", book_id: 6495407})

    // 忽略的字段为 0 或 空
   fmt.Println(Books{title: "Go 语言", author: "www.runoob.com"})
}

依赖注入实现：https://github.com/facebookarchive/inject

简介：Package inject provides a reflect based injector. 基于反射实现

实例：

package main

import (
    "fmt"
    "net/http"
    "os"

    "github.com/facebookgo/inject"
)

type HomePlanetRenderApp struct {
    NameAPI   *NameAPI   `inject:""`
    PlanetAPI *PlanetAPI `inject:""`
}

func (a *HomePlanetRenderApp) Render(id uint64) string {
    return fmt.Sprintf(
        "%s is from the planet %s.",
        a.NameAPI.Name(id),
        a.PlanetAPI.Planet(id),
    )
}

type NameAPI struct {
    // 接口类型 不能被自动创建 所以需要被明确地提供
    HTTPTransport http.RoundTripper `inject:""`
}

func (n *NameAPI) Name(id uint64) string {
    return "Spock"
}

type PlanetAPI struct {
    HTTPTransport http.RoundTripper `inject:""`
}

func (p *PlanetAPI) Planet(id uint64) string {
    return "Vulcan"
}

func main() {
    var g inject.Graph
    var a HomePlanetRenderApp
    err := g.Provide(
        &inject.Object{Value: &a},
        &inject.Object{Value: http.DefaultTransport},
    )
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        os.Exit(1)
    }

    // creating instances
    if err := g.Populate(); err != nil {
        fmt.Fprintln(os.Stderr, err)
        os.Exit(1)
    }

    fmt.Println(a.Render(42))
    fmt.Println(a.NameAPI.HTTPTransport == a.PlanetAPI.HTTPTransport)
}