如何通过map [string] interface {}进行递归迭代

Question

I faced with a problem how to iterate through the map[string]interface{} recursively with additional conditions.

1) if a value is a map - recursively call the method

2) if a value is an array - call method for array

3) if a value isn't a map - process it.

Now when method try to execute doc.throughMap(mv) - error occurs So how can I convert some value to needed type after reflect confirm that value is a map or an array?

type MapType map[string]interface{}
type ArrayType []interface{}
func (doc *Document) throughMap(docMap MapType) MapType {
    for k, v := range docMap {
        vt := reflect.TypeOf(v)
        switch vt.Kind() {
        case reflect.Map:
            if mv, ok := v.(map[string]interface{}); ok {
                docMap[k] = doc.throughMap(mv)
            } else {
                panic("error.")
            }
        case reflect.Array, reflect.Slice:
            if mv, ok := v.([]interface{}); ok {
                docMap[k] = doc.throughArray(mv)
            } else {
                panic("error.")
            }
        default:
            docMap[k] = doc.processType(v)
        }
    }
    return docMap
}

Stacktrace:

panic: error. [recovered]
    panic: error.

goroutine 1 [running]:
encoding/json.(*encodeState).marshal.func1(0xc000074cd0)
    /usr/local/go/src/encoding/json/encode.go:301 +0x9a
panic(0x4bd700, 0x4f9b70)
    /usr/local/go/src/runtime/panic.go:513 +0x1b9
project-name/package/name.(*Document).throughMap(0xc00000c028, 0xc000060180, 0xc00007e000)
    /home/path/to/project/document.go:231 +0x3f4
project-name/package/name.(*Document).convertDocument(0xc00000c028)
    /home/path/to/project/document.go:217 +0x33
project-name/pachage/name.(*Document).MarshalJSON(0xc00000c028, 0x4db740, 0xc00000c028, 0x7f3f0f7540c0, 0xc00000c028, 0xc00001c101)
    /home/path/to/project/document.go:167 +0xd8
encoding/json.marshalerEncoder(0xc00007c000, 0x4db740, 0xc00000c028, 0x16, 0xc000070100)
    /usr/local/go/src/encoding/json/encode.go:453 +0xb7
encoding/json.(*encodeState).reflectValue(0xc00007c000, 0x4db740, 0xc00000c028, 0x16, 0x4c0100)
    /usr/local/go/src/encoding/json/encode.go:333 +0x82
encoding/json.(*encodeState).marshal(0xc00007c000, 0x4db740, 0xc00000c028, 0x4f0100, 0x0, 0x0)
    /usr/local/go/src/encoding/json/encode.go:305 +0xf4
encoding/json.Marshal(0x4db740, 0xc00000c028, 0xc000034698, 0x3, 0x3, 0x4d, 0x0)
    /usr/local/go/src/encoding/json/encode.go:160 +0x52
main.main()
    /home/path/to/project/main.go:21 +0x34d

Answer 1

Use the following code to recurse through maps, arrays and slices of any type:

func walk(v reflect.Value) {
    fmt.Printf("Visiting %v
", v)
    // Indirect through pointers and interfaces
    for v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface {
        v = v.Elem()
    }
    switch v.Kind() {
    case reflect.Array, reflect.Slice:
        for i := 0; i < v.Len(); i++ {
            walk(v.Index(i))
        }
    case reflect.Map:
        for _, k := range v.MapKeys() {
            walk(v.MapIndex(k))
        }
    default:
        // handle other types
    }
}