替代哈希以处理Go中的混合类型

Question

I'm doing a programming exercise to get familiar with Go. I'm currently writing a parser which parses a string into a command with arguments, e.g:

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.

At first I started using hashes to hold the arguments e.g. w h. But this is inflexible and as you can see c is a colour which will be a string, while the other arguments are integers.

I've started like this:

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")
    }
}

My question is how should I go about parsing an input string into a command, if the arguments I want to return are variable and have mixed types? Thanks.

P.S the commands are free typed in and modify a fake canvas in the terminal e.g:

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

Your approach to command isn't right. A command is something you can apply to a canvas. So we say so:

type canvas struct{ ... }

type command interface {
    apply(canvas *canvas)
}

Now there are several kinds of commands, each with its own arguments. When being used as a command, however, the caller shouldn't have to care what those arguments are.

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) { ... }

And then you can parse them (I'd probably pull all the parsing into functions, but this is fine).

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")
    }
}

Note that this return nil as the command when something fails, not command{}.

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