确定删除操作是否实际上删除了映射中的现有键

Question

I have a map called nearby

func Delete(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    delete(nearby, params["id"])
}

I want to find out if the delete() call actually found a key to delete, I tried reading the return value:

func Delete(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    result := delete(nearby, params["id"])
}

but the compiler didn't like that - how can I find out if a key/val was deleted?

Answer 1

Probe the map before deleting the value:

func Delete(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    _, deleted := nearby[params["id"]]
    delete(nearby, params["id"])
    fmt.Println(deleted)
}

This snippet and the code in the question have a data race because HTTP handlers can be called concurrently. Add a mutex to protect the map.

var (
    nearby = make(map[string]string)
    mu     sync.Mutex
)

func Delete(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    mu.Lock()
    _, deleted := nearby[params["id"]]
    delete(nearby, params["id"])
    mu.Unlock()
    fmt.Println(deleted)
}