dongtieshang5429 2018-05-05 15:21
浏览 74
已采纳

是否可以在go插件和应用程序之间共享自定义数据类型?

I know that it is possible to look up for go-plugin symbols that were exported and type assert them into an interface. However, I wonder if is there a way to type assert them into a struct, for example. Is there a way to do it?

For example:

plugin.go

package main

type Person struct {
    Name string
}

var (
    P = Person{
        Name: "Emma",
    }
)

app.go

package main

import (
    "fmt"
    "plugin"
    "os"
)

func main() {
    plug, err := plugin.Open("./plugin.so")
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    sym, err := plug.Lookup("P")
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    var p Person
    p, ok := sym.(Person)
    if !ok {
        fmt.Println("Wrong symbol type")
        os.Exit(1)
    }

    fmt.Println(p.Name) 
}

The symbol P, which is a Person, is found when plug.Lookup is called. However, I can't type-assert P into Person, I get an execution time error. In this example, "Wrong symbol type".

Is there a way to achieve this or the only way to share data between the plugin and the application is using interfaces?

Thanks.

展开全部

  • 写回答

1条回答 默认 最新

  • drui0508 2018-05-23 10:35
    关注

    Identifiers defined in the main package cannot be referred to from other packages, so an exported identifier from a plugin cannot be the same type what you have in your main app. Even if you would duplicate the Person type both in the plugin's file and in your main app, type assertion would fail because they are not the same type!

    But it is possible to define the type in a separate package, and use this same package in the plugin and in the main app. And then you can type assert this type from a symbol you lookup from the plugin.

    See this example:

    The separate type defined in its own package:

    package filter
    
    type Filter struct {
        Name string
        Age  int
    }
    

    Plugin code:

    package main
    
    import (
        "play/filter"
    )
    
    var MyFilter = filter.Filter{
        Name: "Bob",
        Age:  21,
    }
    
    func CreateFilter() filter.Filter {
        return filter.Filter{
            Name: "Bob",
            Age:  21,
        }
    }
    

    The main app:

    package main
    
    import (
        "fmt"
        "log"
        "os"
        "play/filter"
        "plugin"
    )
    
    func main() {
        p, err := plugin.Open("plugin.so")
        if err != nil {
            log.Fatal(err)
        }
        mf, err := p.Lookup("MyFilter")
        if err != nil {
            log.Fatal(err)
        }
        f, ok := mf.(*filter.Filter)
        if !ok {
            log.Fatal("Wrong symbol type")
        }
    
        fmt.Printf("%+v
    ", f)
    }
    

    Running the main app, the output is:

    &{Name:Bob Age:21}
    

    What you may notice is that the exported identifier in the plugin MyFilter is a variable of non-pointer type, yet we type-asserted a pointer type from the exported symbol. This is because if you lookup a variable, you will get a pointer to it, else you could not modify the value of the variable, you could only modify the copy. This is detailed in this answer: Plugin symbol as function return

    This is not the case if we lookup the other symbol our plugin exports: the CreateFilter() function which returns a value of non-pointer type filter.Filter:

    cf, err := p.Lookup("CreateFilter")
    if err != nil {
        log.Fatal(err)
    }
    
    createFilter, ok := cf.(func() filter.Filter)
    if !ok {
        log.Fatal("Wrong function type")
    }
    f2 := createFilter()
    fmt.Printf("%+v
    ", f2)
    

    Running this code, the output will be:

    {Name:Bob Age:21}
    

    See related question: go 1.8 plugin use custom interface

    Also note that if you change the filter package used commonly by the plugin and the main app, you also have to rebuild the plugin. Attempting to run the app without rebuilding the plugin will result in an error during the plugin.Open() call. For details, see How do Go plugin dependencies work?

    展开全部

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论
编辑
预览

报告相同问题?

悬赏问题

  • ¥15 python 用Dorc包报错,我的写法和网上教的是一样的但是它显示无效参数,是什么问题
  • ¥15 指定IP电脑的访问设置
  • ¥30 matlab ode45 未发现警告,但是运行出错
  • ¥15 vscode platformio
  • ¥15 代写uni代码,app唤醒
  • ¥15 全志t113i启动qt应用程序提示internal error
  • ¥15 ensp可以看看嘛.
  • ¥80 51单片机C语言代码解决单片机为AT89C52是清翔单片机
  • ¥60 优博讯DT50高通安卓11系统刷完机自动进去fastboot模式
  • ¥15 minist数字识别
手机看
程序员都在用的中文IT技术交流社区

程序员都在用的中文IT技术交流社区

专业的中文 IT 技术社区,与千万技术人共成长

专业的中文 IT 技术社区,与千万技术人共成长

关注【CSDN】视频号,行业资讯、技术分享精彩不断,直播好礼送不停!

关注【CSDN】视频号,行业资讯、技术分享精彩不断,直播好礼送不停!

客服 返回
顶部