Unable to check nil for a struct referenced as pointer

Getting Help
1 

import (
	"fmt"
)



type str struct {
	a string
}

func main() {

	var p *str
	chk(p)

}

func chk(s interface{}) {
	fmt.Println("Check", s) // HERE IT IS PRINTING NIL
	if s == nil { // BUT HERE I AM UNABLE TO CHECK
		fmt.Println("It is null....")
	}
	fmt.Println("Hello, playground")
}
2

Take a look at this:

package main

import (
	"fmt"
)

type str struct {
	a string
}

func main() {
	var p *str
	chk(p)
}

func chk(s interface{}) {
	fmt.Printf("value=%v type=%t\n", s, s)
	// The type of s is not nil, so the following is false.
	if s == nil {
		fmt.Println("It is null....")
	}
	fmt.Println("Hello, playground")
}

The ouput is

value=<nil> type=%!t(*main.str=<nil>)
Hello, playground

To be nil, both the type and the value must be nil.

See also https://u.lhorn.de/mo3Z.

1 Like
3

Thank you Lutzhorn,

your reply was most useful

and one more thing
How can i check only the value is empty?

4

Try this:

package main

import (
	"fmt"
	"reflect"
)

type str struct {
	a string
}

func main() {
	var p *str
	chk(p)
}

func chk(s interface{}) {
	fmt.Printf("value=%v type=%t\n", s, s)
	// The type of s is not nil, so the following is false.
	if s == nil {
		fmt.Println("s is nil....")
	}
	// The value of s is nil, the following is true.
	if reflect.ValueOf(s).IsNil() {
		fmt.Println("value of s is nil")
	}
	fmt.Println("Hello, playground")
}

Output:

value=<nil> type=%!t(*main.str=<nil>)
value of s is nil
Hello, playground

See also https://u.lhorn.de/m65w.

1 Like
5 

import (
	"fmt"
	"reflect"
)

var string1 string
var int1 int

type strtemp struct {
	newstr string
}
type str struct {
	a  string
	st *strtemp
}

func main() {
	var p *str
	chk(string1)
	chk(int1)
	chk(p)
}

func chk(s interface{}) {
	fmt.Printf("value=%v type=%t\n", s, s)
	// The type of s is not nil, so the following is false.
	if s == nil {
		fmt.Println("s is nil....")
	}
	// The value of s is nil, the following is true.
	if reflect.ValueOf(s).IsNil() {
		fmt.Println("value of s is nil")
	}
	fmt.Println("Hello, playground")
}
6 
panic: reflect: call of reflect.Value.IsNil on string Value

goroutine 1 [running]:
reflect.Value.IsNil(0xee6e0, 0x195920, 0x98, 0x195920, 0x98, 0xf0740)
	/usr/local/go/src/reflect/value.go:1018 +0x160
main.chk(0xee6e0, 0x195920)
	/tmp/sandbox753849162/main.go:33 +0xc0
main.main()
	/tmp/sandbox753849162/main.go:21 +0x60```
7

This is the error i’m facing… i’m trying all type of values

8

int and string can not be used like this. But why do you want to pass them as an interface{}? What are you trying to do?

9

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