结构图不保存键/值

Question

package main

import "fmt"
import "reflect"

type someMap struct {
    X map[string]string
}

func (s *someMap) mapSetter(someKey string, someValue string) {
    s.X = make(map[string]string)
    s.X[someKey] = someValue
}

func (s someMap) mapGetter() map[string]string {
    return s.X
}

func (s someMap) mapKeys() []reflect.Value {
    return reflect.ValueOf(s.X).MapKeys()
}

func retrievedList(x map[string]string) {
    fmt.Println("I got %v", x)
}

func main() {
    v := new(someMap)
    v.mapSetter("item1", "value1")
    v.mapSetter("item2", "value2")
    returnedMap := v.mapGetter()
    fmt.Println(returnedMap)
    fmt.Println(reflect.TypeOf(returnedMap))
    retrievedList(returnedMap)
    fmt.Println(v.mapKeys())
    keys := v.mapKeys()
    fmt.Println(keys[0])
}

As you can see, I'm setting two keys/values to my struct "someMap", however when it looks like the key is overwritten rather than saved, why is this?

map[item2:value2]
map[string]string
I got %v map[item2:value2]
[item2]
item2

I've been following the map examples here https://blog.golang.org/go-maps-in-action

As far I know, which isn't a lot, I'm new to golang, this should work somewhat similar to python.

Answer 1

The reason is that in mapSetter you are overwriting s.X every time with a new instance by calling make(map[string]string). Remove that line from there and either initialize v.X in main:

v.X = make(map[string]string)

Or create a function to both create the new someMap instance and initialize its X:

func New() *someMap {
    s := new(someMap)
    s.X = make(map[string]string)
    return s
}

See here