使用反射获取指向值的指针

Question

I have a function that iterates through all fields of an interface passed as parameter. In order to achieve this is I am using reflection. The issue is that I do not know how to obtain the address of a non-pointer field. Here is an example:

type Z struct {
    Id int
}

type V struct {
    Id int
    F Z
}

type T struct {
    Id int
    F V
}

The above code represents my test structures. Now here is the actual function which traverses a specified structure and lists details about it:

func InspectStruct(o interface{}) {
     val := reflect.ValueOf(o)
     if val.Kind() == reflect.Interface && !val.IsNil() {
        elm := val.Elem()
        if elm.Kind() == reflect.Ptr && !elm.IsNil() && elm.Elem().Kind() == reflect.Ptr {
            val = elm
        }
     }
     if val.Kind() == reflect.Ptr {
        val = val.Elem()
     }

    for i := 0; i < val.NumField(); i++ {
        valueField := val.Field(i)
        typeField := val.Type().Field(i)
        address := "not-addressable"

        if valueField.Kind() == reflect.Interface && !valueField.IsNil() {
            elm := valueField.Elem()
            if elm.Kind() == reflect.Ptr && !elm.IsNil() && elm.Elem().Kind() == reflect.Ptr {
                valueField = elm
            }
        }
        if valueField.Kind() == reflect.Ptr {
            valueField = valueField.Elem()
        }
        if valueField.CanAddr() {
            address = fmt.Sprint(valueField.Addr().Pointer())
        }

        fmt.Printf("Field Name: %s,\t Field Value: %v,\t Address: %v\t, Field type: %v\t, Field kind: %v
", typeField.Name, 
            valueField.Interface(), address, typeField.Type, valueField.Kind())

        if valueField.Kind() == reflect.Struct {
            InspectStruct(valueField.Interface())
        }
    }
}

And here is the actual test after structure instantiation/initialization:

t := new(T)
t.Id = 1
t.F = *new(V)
t.F.Id = 2
t.F.F = *new(Z)
t.F.F.Id = 3

InspectStruct(t)

And finally the output of InspectStruct call:

Field Name: Id,  Field Value: 1,     Address: 408125440 , Field type: int   , Field kind: int
Field Name: F,   Field Value: {2 {3}},   Address: 408125444 , Field type: main.V    , Field kind: struct
Field Name: Id,  Field Value: 2,     Address: not-addressable   , Field type: int   , Field kind: int
Field Name: F,   Field Value: {3},   Address: not-addressable   , Field type: main.Z    , Field kind: struct
Field Name: Id,  Field Value: 3,     Address: not-addressable   , Field type: int   , Field kind: int

As you can see I am using recursion, so if one of the fields is a struct kind then I call InspectStruct for it. My issue is that though all fields have been initialized for the entire structure "t" hierarchy, I am not able to get the address for any field located at a higher depth than "t". I would really appreciate any help.

Answer 1

Passing reflect.Value instead of interface{} seems to fix the problem, however I don't know why valueField.Interface() doesn't work.

Working example : http://play.golang.org/p/nleA2YWMj8

func InspectStructV(val reflect.Value) {
    if val.Kind() == reflect.Interface && !val.IsNil() {
        elm := val.Elem()
        if elm.Kind() == reflect.Ptr && !elm.IsNil() && elm.Elem().Kind() == reflect.Ptr {
            val = elm
        }
    }
    if val.Kind() == reflect.Ptr {
        val = val.Elem()
    }

    for i := 0; i < val.NumField(); i++ {
        valueField := val.Field(i)
        typeField := val.Type().Field(i)
        address := "not-addressable"

        if valueField.Kind() == reflect.Interface && !valueField.IsNil() {
            elm := valueField.Elem()
            if elm.Kind() == reflect.Ptr && !elm.IsNil() && elm.Elem().Kind() == reflect.Ptr {
                valueField = elm
            }
        }

        if valueField.Kind() == reflect.Ptr {
            valueField = valueField.Elem()

        }
        if valueField.CanAddr() {
            address = fmt.Sprintf("0x%X", valueField.Addr().Pointer())
        }

        fmt.Printf("Field Name: %s,\t Field Value: %v,\t Address: %v\t, Field type: %v\t, Field kind: %v
", typeField.Name,
            valueField.Interface(), address, typeField.Type, valueField.Kind())

        if valueField.Kind() == reflect.Struct {
            InspectStructV(valueField)
        }
    }
}

func InspectStruct(v interface{}) {
    InspectStructV(reflect.ValueOf(v))
}