英文:
Retrieving values from nested map in golang
问题
我正在尝试从一个嵌套的 map 中获取一个值。我已经按照在线教程的步骤进行了操作，但是没有得到正确的答案。这是我的程序：
type OptionMap map[string]interface{}
func(options OptionMap) {
opt, _ := options["data2"].(OptionMap)
fmt.Println("opt", opt)
for key, value := range options {
fmt.Println("Key:", key, "Value:", value)
}
}
options 有两个键 data1 和 data2。在 for 循环中，printf 打印出以下内容：
Key: data1 Value: false
Key: data2 Value: map[h:5]
当我运行以下代码时：
opt, _ := options["data2"].(OptionMap)
我得到的 opt 是 nil。我不确定如何获取 map[h:5] 的值。
英文:
I'm trying to retrieving a value from a map within a map. I have followed online tutorials but not getting the right answer. This is my program:
type OptionMap map[string]interface{}
func(options OptionMap) {
opt, _ := options["data2"].(OptionMap)
fmt.Println("opt", opt)
for key, value := range options {
fmt.Println("Key:", key, "Value:", value)
}
}
options has two keys data1 and data2 . Inside for loop the printf prints following
Key: data1 Value: false
Key: data2 Value: map[h:5]
When I run the code
opt, _ := options["data2"].(OptionMap)
I'm getting nil in opt. I'm not sure how to retrieve value of map[h:5].
答案1
得分: 1
你在获取内部映射的值时得到了nil值，这是因为你没有使用OptionMap类型创建内部映射。你可能是使用了map[string]interface{}来创建它，并试图断言为OptionMap类型，但在获取nil值时失败了。请参考下面的示例，该示例也使用了OptionMap类型。请查看类型断言页面：https://tour.golang.org/methods/15
package main
import "fmt"
type OptionMap map[string]interface{}
func main() {
opt := make(OptionMap)
ineeropt := make(OptionMap) // 在创建映射时指定OptionMap类型
ineeropt["h"] = 5
opt["data1"] = false
opt["data2"] = ineeropt
test(opt)
}
func test(options OptionMap) {
opt, _ := options["data2"].(OptionMap) // 如果内部映射是使用OptionMap创建的，则opt不会为nil
fmt.Println("opt", opt)
fmt.Println("opt", options)
for key, value := range options {
fmt.Println("Key:", key, "Value:", value)
}
}
希望对你有帮助！
英文:
You are getting nil value for inner map because you have not created inner map using type OptionMap.You must have created it using map[string]interface{} and trying to assert to OptionMap which is failing in getting nil value. See below example which is working with OptionMap type,too.Go through type assertion page at https://tour.golang.org/methods/15
package main
import "fmt"
type OptionMap map[string]interface{}
func main() {
opt := make(OptionMap)
ineeropt := make(OptionMap) // while creating Map specify OptionMap type
ineeropt["h"]=5
opt["data1"] = false
opt["data2"] = ineeropt
test(opt)
}
func test(options OptionMap) {
opt, _ := options["data2"].(OptionMap) //If inner map is created using OptionMap then opt won't be nil
fmt.Println("opt", opt)
fmt.Println("opt", options)
for key, value := range options {
fmt.Println("Key:", key, "Value:", value)
}
}
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