Golang nil pointer dereference •

Go: panic: runtime error: invalid memory address or nil pointer dereference

Problem statement

Sample code

type Calculate struct {
  X, Y int64
}

func (c *Calculate) Sum() int64 {
  return c.X + c.Y
}

func main() {
  var cal *Calculate //  Initialize cal to <nil>
  fmt.Println("SUM =", cal.Sum()) // calling method on <nil> creates panic
 }
}

Running code:

go run main.go

Output:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x497783]

goroutine 1 [running]:
main.(*Calculate).Sum(...)
  /tmp/sandbox800773077/prog.go:12
main.main()
  /tmp/sandbox800773077/prog.go:17 +0x23

Why is issue:

The uninitialized pointer “cal” in the main function is nil, and so can’t call method on the nil pointer. If “cal” is nil, an attempt to evaluate “*cal” will cause a run-time panic.

Solution

func main() {
  var cal *Calculate = new(Calculate) // Initialize cal to &{0 0}
  fmt.Println("SUM".cal.Sum()) // calling method cal Worked
}

Output :

SUM = 0

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