如何通过Golang的组合继承将command分派到正确的CommandHandler

Question

我想学习在Go编程，我决定作为一个宠物程序，我会做一个简单的调度不同的命令几个CommandHandler(如果CommandHandler有相同的名称，它应该处理的命令)

我的问题是，当我想有一个CommandHandlerManager发布一个命令，将被调度到正确的CommandHandler，它告诉我，我需要有我的HelloWorldCommand的具体实现，因为HelloWorldCommandHandler不实现命令的接口。

编译错误信息

E:DesktopManBeargolangsrc>go run main.go
# command-line-arguments
.main.go:71: cannot use cmdHandler (type HelloWorldCommandHandler) as type CommandHandler in array or slice literal:
        HelloWorldCommandHandler does not implement CommandHandler (wrong type for Handle method)
                have Handle(HelloWorldCommand)
                want Handle(Command)

我需要有人解释我做错了什么，我猜这意味着我应该实现一个单独的func方法到我的HelloWorldCommandHandler单独的接口，如下所示:

func (ch HelloWorldCommandHandler) Handle(cmd Command) {
    fmt.Println("HelloWorldCommandHandler handled the basic command with name --> " + cmd.GetName())
}

但是它产生了更多与类型相关的错误。

给我一个例子，说明我正在做什么，并解释我是如何以及为什么做错了，我将不胜感激。

谢谢。下面是我的代码:

package main 
import (
    "fmt"
    "strconv"
)

type Command interface {
    GetName() string
}

type CommandHandler interface {
    Command
    Handle(cmd Command)
}

type HelloWorldCommand struct {
    Command
    Name string
    Age int
}
func (cmd HelloWorldCommand) GetName() string {
    return "HelloWorldCommand"
}

type HelloWorldCommandHandler struct {
    CommandHandler
}
func (cmd HelloWorldCommandHandler) GetName() string {
    return "HelloWorldCommand"
}
func (ch HelloWorldCommandHandler) Handle(cmd HelloWorldCommand) {
    fmt.Println("Hello World! My name is " + cmd.Name + " and I'm " + strconv.Itoa(cmd.Age) + " years old!")
}
type CommandHandlerManager struct {
    CommandHandlers []CommandHandler
}
func (chm CommandHandlerManager) Publish(cmd Command) {
    for _, cmdHandler := range chm.CommandHandlers {
        if cmd.GetName() == cmdHandler.GetName() {
            cmdHandler.Handle(cmd)
        }
    }
}

func main() {
    fmt.Println("Hey my friend!")
    cmd := HelloWorldCommand {Name: "ManBear", Age: 357}
    cmdHandler := HelloWorldCommandHandler {}
    fmt.Println(cmd.GetName())
    fmt.Println(cmdHandler.GetName())
    cmdHandler.Handle(cmd)
    cmdHandlerManager := CommandHandlerManager { 
        CommandHandlers: []CommandHandler { 
            cmdHandler, // <-- the error is here 
        },
    };
}

更新:

对于好奇的人来说，这里是我的宠物程序的功能版本

多亏了Dean Elbaz的帮助，他建议使用类型断言，这使得通过正确的CommandHandler处理命令并使用每个命令附带的正确值集成为可能。

package main
import (
    "fmt"
    "strconv"
    "time"
)

type Command interface {
    GetName() string
}

type CommandHandler interface {
    Command
    Handle(cmd Command)
}
const HelloWorldCommandName string = "HelloWorldCommand"
type HelloWorldCommand struct {
    Command
    Name string
    Age int
}
func (cmd HelloWorldCommand) GetName() string {
    return HelloWorldCommandName
}
// Basic Hello World
type HelloWorldCommandHandler struct {
    CommandHandler
}
func (cmd HelloWorldCommandHandler) GetName() string {
    return HelloWorldCommandName
}
func (ch HelloWorldCommandHandler) Handle(cmd Command) {
    fmt.Println("Hello World!n----------------------------------------n")
}
// Hello World with Name and Age
type HelloWorldWithNameAndAgeCommandHandler struct {
    CommandHandler
}
func (cmd HelloWorldWithNameAndAgeCommandHandler) GetName() string {
    return HelloWorldCommandName
}
func (ch HelloWorldWithNameAndAgeCommandHandler) Handle(cmd Command) {
    var helloWorldCommand HelloWorldCommand = cmd.(HelloWorldCommand)
    fmt.Println("Hello World! My name is " + helloWorldCommand.Name + " and I'm " + strconv.Itoa(helloWorldCommand.Age) + " years old!n----------------------------------------n")
}

const TodayDateTimeCommandName string = "TodayDateTimeCommand"
// Today's DateTime Command
type TodayDateTimeCommand struct {
    Command
    TimeZone string
}
func (cmd TodayDateTimeCommand) GetName() string {
    return TodayDateTimeCommandName
}

type TodayDateTimeCommandHandler struct {
}
func (ch TodayDateTimeCommandHandler) GetName() string {
    return TodayDateTimeCommandName
}
func (ch TodayDateTimeCommandHandler) Handle(cmd Command) {
    var todayCommand TodayDateTimeCommand = cmd.(TodayDateTimeCommand)
    location, err := time.LoadLocation(todayCommand.TimeZone)
    if err != nil {
        fmt.Errorf("Could not load the Location of the TimeZone. %f", err.Error())
        return
    }
    current_time := time.Now().In(location)
    fmt.Println("Today's date and time is " + current_time.String() + " for the time zone: " + todayCommand.TimeZone)
}

// The CommandHandler Manager
type CommandHandlerManager struct {
    CommandHandlers []CommandHandler
}
func (chm CommandHandlerManager) Publish(cmd Command) {
    for _, cmdHandler := range chm.CommandHandlers {
        if cmd.GetName() == cmdHandler.GetName() {
            cmdHandler.Handle(cmd)
        }
    }
}

func main() {
    fmt.Println("Hey my friend!nnn")
    cmdHandlerManager := CommandHandlerManager {
        CommandHandlers: []CommandHandler {
            HelloWorldCommandHandler {},
            HelloWorldWithNameAndAgeCommandHandler {},
            TodayDateTimeCommandHandler {},
        },
    };
    cmd := HelloWorldCommand {Name: "ManBear", Age: 357}
    cmdHandlerManager.Publish(cmd)
    fmt.Println("~~~~~~~~ other command published ~~~~~~~~~~~~~~~~~~~~~")
    cmd2 := TodayDateTimeCommand{ TimeZone: "America/Montreal" }
    cmdHandlerManager.Publish(cmd2)
}

Answer 1

Handle的签名必须完全是func (ch HelloWorldCommandHandler) Handle(cmd Command) {才能实现接口。一种快速修复方法是在Handle函数的开始处进行类型断言，以从Command

中获取HelloWorldCommand。

但我认为这可能是一个可能的设计问题的症状:如果多态性是在Command上，也许命令应该处理/运行自己?也许有一个Run() error的界面?