类型为嵌套的map [string] interface {}的映射返回"type interface {}不支持索引". [英] Typed, nested map of map[string]interface{} returns "type interface {} does not support indexing"

问题描述

我在键入嵌套地图时遇到了一个非常奇怪的问题.

I'm experiencing a very strange problem with typed nested maps.

gore version 0.2.6  :help for help
gore> type M map[string]interface{}
gore> m := M{"d": M{}}
main.M{"d":main.M{}}
gore> m["d"]["test"] = "will fail"
# command-line-arguments
/tmp/288178778/gore_session.go:13:8: invalid operation: m["d"]["test"] (type interface {} does not support indexing)
/tmp/288178778/gore_session.go:14:17: invalid operation: m["d"]["test"] (type interface {} does not support indexing)
error: exit status 2
exit status 2
gore> m["e"] = "this works"
"this works"
gore> m
main.M{"d":main.M{}, "e":"this works"}

我做错了什么?为什么仅由于将地图嵌套在地图中而突然失败?

What am I doing wrong? Why does this suddenly fail just because the map is nested inside a map?

推荐答案

让我们来看看:

foo:=map[string]interface{}{}

定义 map [string] interface {} 时，可以设置所需的任何类型(满足

When you define a map[string]interface{}, you can set any type you want (any type that fulfill the empty interface interface{} contract a.k.a any type) for a given string index.

foo["bar"]="baz"
foo["baz"]=1234
foo["foobar"]=&SomeType{}

但是当您尝试访问某些键时，您没有得到任何int，字符串或任何自定义结构，而是得到了 interface {}

But when you try to access some key, you don't get some int, string or any custom struct, you get an interface{}

var bar string = foo["bar"] // error

为了将 bar 视为字符串，您可以创建类型断言或类型切换.

in order to treat bar as an string, you can make a type assertion or a type switch.

在这里我们进行类型断言(实时示例):

Here we go for the type assertion (live example) :

if bar,ok := foo["bar"].(string); ok {
   fmt.Println(bar)
}

但是正如@Volker所说的，作为一个初学者，最好采取旅行的旅程以更熟悉这些概念.

But as @Volker said, it is a good idea -as a beginner- to take the tour of go to get more familiar with such concepts.

这篇关于类型为嵌套的map [string] interface {}的映射返回"type interface {}不支持索引".的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！