Go Unmarshal reflect.Type got map[string]interface{}

I want to convert json string to some struct ,use as func param
I use reflect to get Param Type,this work fine ,
but if I use json.Unmarshal I always get map[string]interface{}

this is a mini Run sample,File name is json_test.go

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package testJson

import (
	"reflect"
	"encoding/json"
	"testing"
	"log"
)

type LoginForm struct {
	Name string
}

func Login(login LoginForm) {

}

func TestRun(t *testing.T) {
	_func := Login
	f := reflect.ValueOf(_func)
	funcType := f.Type()
	paramType := funcType.In(0)
	log.Print(paramType.Name())
	v := reflect.New(paramType).Elem().Interface()
	jsonstr := `{"Name":"123"}`
	log.Print(jsonstr)
	log.Print(reflect.TypeOf(v).Name())
	log.Print("%+v", v)
	err := json.Unmarshal([]byte(jsonstr), &v)
	if err != nil {
		panic(err)
	}
	log.Print(reflect.TypeOf(v).Name())
	log.Print( v)
	var in []reflect.Value
	in = make([]reflect.Value, funcType.NumIn())
	in[0] = reflect.ValueOf(v)
	f.Call(in)
}

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Thanks for your help!

Don't reflect.New a pointer type because the result of that is a pointer to the pointer, instead reflect.New the Elem of the pointer type.

Change this:

v := reflect.New(paramType).Elem().Interface()

To this:

v := reflect.New(paramType.Elem()).Interface()

At this point v is already a pointer to LoginForm so you don't need to get its address with & when passing to Unmarshal.

https://play.golang.org/p/JM4fRXb7fo

Also the reason you got map[string]interface{} is because the return type of the Interface() method is unsurprisingly enough interface{}, so while v's underlying type could be anything its "topmost" type is interface{}. So then, doing &v will get you *interface{} as opposed to the inteded *LoginForm. And in the docs you can find that trying to unmarshal a JSON object into an interface{} will result in a value of type map[string]interface{}.