go文档模式，编译出错，各位道友帮忙看看

```console github.com/meijies/theme/collection/config ./document.go:21:29: cannot assign to struct field target.sub[subkey].value in map ./document.go:23:11: cannot use target.sub[subkey] (type doc) as type *doc in assignment ./document.go:33:10: cannot use target.sub[subkey] (type doc) as type *doc in assignment FAIL command-line-arguments [build failed] ```

```go package config import "strings" type doc struct { value string sub map[string]doc } var root = new(doc) func Add(key string, value string) { keys := strings.Split(key, ".") var target = root for index, subkey := range keys { if target.sub == nil { target.sub = make(map[string]doc) target.sub[subkey] = doc{} } if index == len(keys)-1 { target.sub[subkey].value = value } else { target = target.sub[subkey] } } } func Get(key string) string { keys := strings.Split(key, ".") target := root for index, subkey := range keys { target = target.sub[subkey] if index == len(keys)-1 { return target.value } } return "" } ```