在Go中使用包含切片字段的结构作为映射键的惯用方式是什么？

Question

I have a struct that contains a slice and I would like to use it as a key to a map. I understand that this is not allowed because equality is not currently defined for slices in Go. I also know that I can't override equality for the struct to do the slice comparison by hand. My question is: what is the most idiomatic way to accomplish what I'm trying to do here?

This is a bit of example code that makes the structure more clear:

package main

import "fmt"

type InternalStruct struct {
    item1, item2 bool
}

type ContainerStruct struct {
    internals []InternalStruct
}

func main() {
    container1 := ContainerStruct{}
    container1.internals = append(container1.internals, InternalStruct{item1: true})

    container2 := ContainerStruct{}
    container2.internals = append(container2.internals, InternalStruct{item1: true})

    m := make(map[ContainerStruct]int)
    m[container1] = 10

    fmt.Printf("container1 maps to: %d
", m[container1])
    fmt.Printf("container1 maps to: %d
", m[container2])
}

This code doesn't compile (as expected), but I'm looking for something equivalent that would output "10" twice. What's the best way to go about achieving this result?

Answer 1

You cannot use slice as a map key, but if you know the size of such slices, you may use arrays instead. Arrays are allowed to be map keys.

package main

import "fmt"

func main() {
    m := make(map[[2]int]int)

    m[[2]int{1, 2}] = 3
    m[[2]int{3, 4}] = 1

    fmt.Println(m)
}

Playground