Question

我正在进行编程练习以熟悉Go。我目前正在编写一个解析器，该解析器将字符串解析为带有参数的命令，例如：

C w h           Should create a new canvas of width w and height h.
B x y c         Should fill the entire area connected to (x,y) with "colour" c.
Q               Should quit the program.

起初我开始使用散列来保存参数，例如w h。但这是不灵活的，您可以看到c是一种颜色，它将是一个字符串，而其他参数是整数。

我是这样开始的：

package main

import (
    "errors"
    "strconv"
    "strings"
)

type command struct {
    id   string
    args map[string]int // Won't work because args can be of mixed types
}

func parseCommand(input string) (command, error) {
    if input == "" {
        return command{}, errors.New("No input")
    }

    commandParts := strings.Split(input, " ")

    switch commandParts[0] {
    case "C":
        if (len(commandParts)) != 3 {
            return command{}, errors.New("C (create) requires 2 arguments")
        }

        w, err := strconv.Atoi(commandParts[1])

        if err != nil {
            return command{}, errors.New("width must be an integer")
        }

        h, err := strconv.Atoi(commandParts[2])

        if err != nil {
            return command{}, errors.New("height must be an integer")
        }

        return command{
            id: "create",
            args: map[string]int{
                "w": w,
                "h": h,
            },
        }, nil
    case "B":
        if (len(commandParts)) != 4 {
            return command{}, errors.New("B (Bucket Fill) requires 3 arguments")
        }

        x, err := strconv.Atoi(commandParts[1])

        if err != nil {
            return command{}, errors.New("x must be an integer")
        }

        y, err := strconv.Atoi(commandParts[2])

        if err != nil {
            return command{}, errors.New("y must be an integer")
        }

        return command{
            id: "bucketFill",
            args: map[string]int{
                "x": x,
                "y": y,
                "c": commandParts[3], // This should be a string!
            },
        }, nil
    case "Q":
        return command{
            id: "quit",
        }, nil
    default:
        return command{}, errors.New("Command not supported")
    }
}

我的问题是，如果要返回的参数是变量且具有混合类型，我应该如何将输入字符串解析为命令？谢谢。

PS可以自由键入命令并在终端中修改假画布，例如：

enter command: C 20 4
----------------------
|                    |
|                    |
|                    |
|                    |
----------------------

// Didn't mention this one but it's a Line if you didn't guess
enter command: L 1 2 6 2
----------------------
|                    |
|xxxxxx              |
|                    |
|                    |
----------------------

Answer 1

您对command的处理方式不正确。 command是可以应用于画布的东西。所以我们这样说：

type canvas struct{ ... }

type command interface {
    apply(canvas *canvas)
}

现在有几种命令，每种命令都有自己的参数。但是，当用作命令时，调用者不必关心那些参数是什么。

type createCommand struct {
    width  int
    height int
}

func (c createCommand) apply(canvas *canvas) { ... }

type bucketFillCommand struct {
    x     int
    y     int
    color string
}

func (c bucketFillCommand) apply(canvas *canvas) { ... }

type quitCommand struct{}

func (c quitCommand) apply(canvas *canvas) { ... }

然后您可以解析它们（我可能会将所有解析放入函数中，但这很好）。

func parseCommand(input string) (command, error) {
    if input == "" {
        return nil, errors.New("No input")
    }

    commandParts := strings.Split(input, " ")

    switch commandParts[0] {
    case "C":
        if (len(commandParts)) != 3 {
            return nil, errors.New("C (create) requires 2 arguments")
        }

        w, err := strconv.Atoi(commandParts[1])

        if err != nil {
            return nil, errors.New("width must be an integer")
        }

        h, err := strconv.Atoi(commandParts[2])

        if err != nil {
            return nil, errors.New("height must be an integer")
        }

        return createCommand{width: w, height: h}, nil
    case "B":
        if (len(commandParts)) != 4 {
            return nil, errors.New("B (Bucket Fill) requires 3 arguments")
        }

        x, err := strconv.Atoi(commandParts[1])

        if err != nil {
            return nil, errors.New("x must be an integer")
        }

        y, err := strconv.Atoi(commandParts[2])

        if err != nil {
            return nil, errors.New("y must be an integer")
        }

        return bucketFillCommand{x: x, y: y, color: commandParts[3]}, nil
    case "Q":
        return quitCommand{}, nil
    default:
        return nil, errors.New("Command not supported")
    }
}

请注意，如果某件事失败，则返回nil作为命令，而不是command{}。

Playground

替代哈希以处理Go中的混合类型

1 个答案: