为什么 map value 是 struct 的时候 无法改变 struct 的变量呢? 迷惑啊

[admirez]

type data struct {
name string
}

func main() {
m := map[string]data {"x":{"one"}}
m["x"].name = "two" //cannot assign to struct field m["x"].name in map
}

[btjoker]

因为你取到的是复制品啊
m := map[string]data {
"x": data {"one"}
}
n := data {"two"}
m[x] = n

[btjoker]

不好意思, 引号和逗号掉了
雨痕的 Go 学习笔记, 建议看看

[fuxiaohei]

https://golang.org/ref/spec#Assignments

Each left-hand side operand must be addressable, a map index expression, or (for = assignments only) the blank identifier. Operands may be parenthesized.

https://golang.org/ref/spec#Address_operators

For an operand x of type T, the address operation &x generates a pointer of type *T to x. The operand must be addressable, that is, either a variable, pointer indirection, or slice indexing operation; or a field selector of an addressable struct operand; or an array indexing operation of an addressable array. As an exception to the addressability requirement, x may also be a (possibly parenthesized) composite literal. If the evaluation of x would cause a run-time panic, then the evaluation of &x does too.

赋值的对象必须是 addressable，用 *T 吧

[laike9m]

https://stackoverflow.com/questions/32751537/why-do-i-get-a-cannot-assign-error-when-setting-value-to-a-struct-as-a-value-i

[admirez]

嗯，用*T 搞定了

[ox180]

```
func main(){
type data struct {
name string
}


s := make(map[int]*data)

s[1] = &data{name: "aa"}

s[1].name = "bb"

fmt.Println(*s[1])

}
```