In golang want a plugins system with a global registry. Structure can be simplified as follows:

/plugins/registry.go
/plugins/plugin1/impl.go

registry.go:

package plugins

import "plugins/plugin1" // required for plugin1.MakePlugin

type IPlugin interface {
  Register() error
}

type Factory func(x int) IPlugin

var registry = []Factory{
  plugin1.MakePlugin,
}

impl.go:

package plugin1

import "plugins" // required for IPlugin

type Plugin struct {
  x int
}

func MakePlugin(x int) plugins.IPlugin {
  return &Plugin{
    x: x,
  }
}

How to solve without moving IPlugin to 3rd (e.g common) package?

PS. I thought if i return *Plugin from MakePlugin this will be compatible with Factory, but its not!!!

CodePudding user response：

"How to solve without moving IPlugin to 3rd (e.g common) package?"

You have at least two options:

1. move the registration to a 3rd (e.g. main) package.
2. have each plugin register itself when imported by some other package.

Example #1

package plugins

type IPlugin interface {
  Register() error
}

type Factory func(x int) IPlugin

var registry []Factory

func Register(ff ...Factory) {
    registry = append(registry, ff...)
}

package main

import (
    "plugins"
    "plugins/plugin1"
)

func init() {
    plugins.Register(plugin1. MakePlugin)
}

func main() {
    // ...
}

Example #2

package plugins

type IPlugin interface {
  Register() error
}

type Factory func(x int) IPlugin

var registry []Factory

func Register(ff ...Factory) {
    registry = append(registry, ff...)
}

package plugin1

import "plugins" // required for IPlugin

func init() {
    plugins.Register(MakePlugin)
}

type Plugin struct {
  x int
}

func MakePlugin(x int) plugins.IPlugin {
  return &Plugin{
    x: x,
  }
}

package main

import (
    "plugins"
    _ "plugins/plugin1" // will execute init() i.e. register
)

func main() {
    // ...
}

CodePudding user response：

Try to separate the Interfaces from their implementation to external packages that are abstract. Then, depend on them according to the Dependency injection and Adapter pattern paradigms.