英文:
Although maps are always reference types, what if they're returned from a non-pointer receiver?
问题
据说在Go语言中，地图（maps）是引用类型，因此当从函数中返回地图时，不需要将地图作为指针传递，以便在函数外部看到更改。但是，如果该地图是从非指针结构体的方法中返回的呢？
例如：
type ExampleMapHolder struct {
theUnexportedMap map[string]int
}
func (emp ExampleMapHolder) TheMap() map[string]int {
return emp.theUnexportedMap
}
如果我调用TheMap()，然后修改其中的一个值，即使接收器不是指针，这个更改是否会在其他地方可见？我想它会返回一个属于ExampleMapHolder副本的地图的引用，但是在文档中没有找到明确的答案。
英文:
Supposedly maps are reference types in Go, so when returning them from functions, you don't need to pass as a pointer to the map in order for the changes to be visible outside the function body. But what if said map is returned from a method on a non-pointer struct?
For example:
type ExampleMapHolder struct {
theUnexportedMap map[string]int
}
func (emp ExampleMapHolder) TheMap() map[string]int {
return emp.theUnexportedMap
}
If I make a call to TheMap(), and then modify a value in it, will this change be visible elsewhere even though the receiver is not a pointer? I imagine it would return a reference to a map that belonged to a copy of ExampleMapHolder, but haven't been able to find an explicit answer in the docs.
答案1
得分: 2
为什么你不直接检查一下呢？
emp := ExampleMapHolder{make(map[string]int)}
m := emp.TheMap()
m["a"] = 1
fmt.Println(emp) // 输出 {map[a:1]}
Playground: http://play.golang.org/p/jGZqFr97_y
英文:
Why won't you just check it?
emp := ExampleMapHolder{make(map[string]int)}
m := emp.TheMap()
m["a"] = 1
fmt.Println(emp) // Prints {map[a:1]}
Playground: http://play.golang.org/p/jGZqFr97_y
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