1.out

$ go run 13.go
main.A{A:0}
main.A{A:0}
main.A{A:1}
(*main.A)(nil)
(*main.A)(nil)
&main.A{A:1}

13.go

package main

import (
	"encoding/json"
	"fmt"
)

type A struct {
	A int
}

func main() {
	a := A{}
	data1 := []byte("null")
	data2, _ := json.Marshal(A{1})
	fmt.Printf("%#v\n", a)
	json.Unmarshal(data1, &a)
	fmt.Printf("%#v\n", a)
	json.Unmarshal(data2, &a)
	fmt.Printf("%#v\n", a)

	b := (*A)(nil)
	fmt.Printf("%#v\n", b)
	json.Unmarshal(data1, &b)
	fmt.Printf("%#v\n", b)
	json.Unmarshal(data2, &b)
	fmt.Printf("%#v\n", b)
}