使用req.Body中的值更新内存中的对象

I am creating a simple in-memory server before doing things with a database. I have this update method:

type Nearby struct {
    ID          int   `json:"id,omitempty"`
    Me          int   `json:"me,omitempty"`
    You         int   `json:"you,omitempty"`
    ContactTime int64 `json:"contactTime,omitempty"`
}

    func (h NearbyHandler) updateById(v NearbyInjection) http.HandlerFunc {
        return func(w http.ResponseWriter, r *http.Request) {
            params := mux.Vars(r)
            decoder := json.NewDecoder(r.Body)
            var t Nearby
            err := decoder.Decode(&t)
            if err != nil {
                panic(err)
            }
            mtx.Lock()
            item, ok := v.Nearby[params["id"]]
            mtx.Unlock()

            if !ok {
                panic(errors.New("No item to update"))
            }

            // !! Ok, how can I overwrite the properties from t onto item

            if ok {
                json.NewEncoder(w).Encode(item)
            } else {
                io.WriteString(w, "null")
            }
        }
    }

I am looking to take the key/values from t, and write them onto the item object. t gets decoded into a struct value (I assume), and item is a struct value found in a map. Both item and t have the same type (Nearby)

In JavaScript, all I am looking to do would be:

Object.assign(item, t);

Just trying to accomplish something similar with Go.

With Golang, I can do this:

    item.ContactTime = t.ContactTime

but I only want to overwrite item.ContactTime if t.ContactTime is defined.

Just overwrite the item in your map:

v.Nearby[params["id"]] = t

I'd suggest to use https://github.com/imdario/mergo function Merge. I don't think there is any reason to reinvent the wheel in this one and go's lack of generics does not help with such operations. example:

src := Foo{
    A: "one",
    B: 2,
}
dest := Foo{
    A: "two",
}
mergo.Merge(&dest, src)
fmt.Println(dest)
// Will print
// {two 2}

I also think you should make all Nearby's properties pointers so that you can always compare them against nil to make sure they were not set.