How to check pointer or interface is nil or not in Golang?

Last Updated : 10 May, 2020

In Golang, nil check is frequently seen in GoLang code especially for error check. In most cases, nil check is straight forward, but in interface case, it’s a bit different and special care needs to be taken.

Here the task is to check pointer or interface is nil or not in Golang, you can check with the following:

Example 1: In this example, the pointer is checked whether it is a nil pointer or not.

// Go program to illustrate how to 
// check pointer is nil or not 
  
package main 
  
import ( 
    "fmt"
) 
  
type Temp struct { 
} 
  
func main() { 
    var pnt *Temp // pointer 
    var x = "123"
    var pnt1 *string = &x 
  
    fmt.Printf("pnt is a nil pointer: %v\n", pnt == nil) 
    fmt.Printf("pnt1 is a nil pointer: %v\n", pnt1 == nil) 
} 

Output:

pnt is a nil pointer: true
pnt1 is a nil pointer: false

Example 2: In this example, the interface is checked whether it is a nil interface or not.

// Go program to illustrate how to 
// check interface is nil or not 
  
package main 
  
import ( 
    "fmt"
) 
  
// Creating an interface 
type tank interface { 
  
    // Methods 
    Tarea() float64 
    Volume() float64 
} 
  
type myvalue struct { 
    radius float64 
    height float64 
} 
  
// Implementing methods of 
// the tank interface 
func (m myvalue) Tarea() float64 { 
  
    return 2*m.radius*m.height + 
        2*3.14*m.radius*m.radius 
} 
  
func (m myvalue) Volume() float64 { 
  
    return 3.14 * m.radius * m.radius * m.height 
} 
  
func main() { 
  
    var t tank 
    fmt.Printf("t is a nil interface: %v\n", t == nil) 
  
    t = myvalue{10, 14} 
  
    fmt.Printf("t is a nil interface: %v\n", t == nil) 
  
} 

Output:

t is a nil interface: true
t is a nil interface: false

Example 3: In this example, the interface holding a nil pointer is checked whether it is a nil interface or not.

// Go program to illustrate how to 
// check interface holding a nil 
// pointer is nil or not 
  
package main 
  
import ( 
    "fmt"
) 
  
type Temp struct { 
} 
  
func main() { 
  
    // taking a pointer 
    var val *Temp 
  
    // taking a interface 
    var val2 interface{} 
  
    // val2 is a non-nil interface 
    // holding a nil pointer (val) 
    val2 = val 
  
    fmt.Printf("val2 is a nil interface: %v\n", val2 == nil) 
  
    fmt.Printf("val2 is a interface holding a nil"+ 
            " pointer: %v\n", val2 == (*Temp)(nil)) 
} 

Output:

val2 is a nil interface: false
val2 is a interface holding a nil pointer: true

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