使用Go语言将地图嵌入到结构中

Question

So in this answerhere, it's stated that one cannot embed a map into a struct in go. However, I was fiddling around with it, and came up with this and it does actually work, and is pretty straight forward.

    package main

import (
    "fmt"
    "runtime"
)

type record struct {
    m map[string]int
}




func main() {
    practice := record{m:make(map[string]int)}
    practice.m["foo"] = 2
    fmt.Println(practice.m)
    runtime.GC()
}

this prints map[foo:2]

However, my question is that, are there any negative sides to using this implementation of maps in structs, or are is there more efficient ways to do this?

Answer 1

1. You can do that, it's absolutely fine.

2. That isn't "embedding". Embedding means something specific — including a nameless field of a named type in a struct. Your map isn't embedded, it's a regular member with the name "m".

3. The answer that you linked is slightly misleading: the answer to the question there ("can I flatten this JSON output without a MarshalJSON method") is indeed no, but it's not actually true that embedding a map in a struct is forbidden. If you create a named type that is a map type, you can embed it in a struct just fine. It just doesn't output in JSON the way that the person asking that question would have liked.