I find the reason, the number's address is not equal with t's address

func main() {
	var number int = 3
	var t interface{} = number
	fmt.Println(&number,&t) //Not equal.
}

So I read the document of reflect, but I don't find any function that can get the pointer of the value that the interface point to.
Is there no way to get number 's address by interface t ?

No, there's no way to get the "address" of a int. That isn't a sensible thing to ask for. Particularly, t does not contain any information about where its value (3) came from. The value '3' is the only thing in the interface, just as if you did

var t interface{} = 3

You could do

var t interface{} = &number

That would provide something you could compare successfully with &number.

No, there's no way to get the "address" of a int. That isn't a sensible thing to ask for. Particularly, t does not contain any information about where its value (3) came from. The value '3' is the only thing in the interface, just as if you did

var t interface{} = 3

You could do

var t interface{} = &number

That would provide something you could compare successfully with &number.

@randall77
My example above is not suitable, please check the original example.

https://go.dev/play/p/7MsCSlPDT6s

package main

import (
	"fmt"
	"reflect"
)

type Data struct {
	Name string `json:"name"`
	Age  int    `json:"age"`
}

func PickData() interface{} {
	return Data{
		Name: "Test",
		Age:  30,
	}
}

func main() {
	t := PickData()
	tValue := reflect.ValueOf(t)
	newData := reflect.NewAt(tValue.Type(), reflect.ValueOf(&t).UnsafePointer()).Interface()
        // Crashed
	fmt.Println(newData.(*Data))
}

It is a sensible thing when using json.Unmarshal.

https://go.dev/play/p/aLNyxR_tmwf

package main

import (
	"encoding/json"
	"fmt"
	"reflect"
)

type Data struct {
	Name string `json:"name"`
	Age  int    `json:"age"`
}

func PickData() interface{} {
	return Data{
		Name: "Test",
		Age:  30,
	}
}

func main() {
	jsonData := []byte(`{"name":"NewName","age":18}`)
        // I can't determine the type of the return of PickData() ,but I can confirm that it must be a struct.
	t := PickData()
	// It changes the t to map[string]interface{}
	// json.Unmarshal(jsonData, &t)

	// So I want to get the pointer of the Data struct so that I can unmarshal to the struct instead of map[string]interface{}.
	pointer := reflect.NewAt(reflect.ValueOf(t).Type(), reflect.ValueOf(&t).UnsafePointer()).Interface()
	// But it crashes if I print the pointer.
	fmt.Println(pointer.(*Data))
	json.Unmarshal(jsonData, pointer)
	fmt.Println(pointer.(*Data))
}

Although I can make a new pointer by this:

func main() {
	jsonData := []byte(`{"name":"NewName","age":18}`)
	t := PickData()

	// I need make a new pointer.
	pointer := reflect.New(reflect.TypeOf(t)).Interface()
	fmt.Println(pointer)
	json.Unmarshal(jsonData, &pointer)
	fmt.Println(pointer)
}

I have to defined a new variable which cost more memory if the struct is so huge.
so I think unsafe or reflect should have ability to access the pointer of data in interface.

This is just a bug in how you're using NewAt.

newData := reflect.NewAt(tValue.Type(), reflect.ValueOf(&t).UnsafePointer()).Interface()

&t has type *interface{}, it does not have type *Data. You're effectively casting it to a *Data forcibly anyway using unsafe, and that will lead to very bad things™.

It's pretty clear this is not a bug in Go, You might want to ask your question in one of the forums listed here, they will probably be of more help.