Function in GoLang

Function

What is a function in GoLang?

function is a self-contained block of code that encapsulates a specific task or related group of tasks.

Function Syntax

func function_name( [parameter list] ) [return_types] {

body of the function

}

Function Example

package main
import "fmt"
func main() {
/* local variable definition */
  var a int = 100
  var b int = 200
  var ret int
  /* calling a function to get max value */
  ret = max(a, b)
  fmt.Printf( "Max value is : %d\n", ret )
}
/* function returning the max between two numbers */
func max(num1, num2 int) int {
/* local variable declaration */
  var result int
  if (num1 num2) {
    result = num1
  } else {
    result = num2
  }
  return result
}

Output

Max value is : 200

Function Return Multiple Values

GoLang function can return multiple values.

package main
import "fmt"
func swap(x, y string) (string, string) {
  return y, x
}
func main() {
  a, b := swap("Nitish", "Kumar")
  fmt.Println(a, b)
}

Output:

Kumar Nitish

Function as Values

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GoLang function can be assigned to variables and passed to or returned from other functions.

package main
import "fmt"
func main() {
  /* declare a function variable */
  getSquareRoot := func(x float64) float64 {
    return math.Sqrt(x)
  }
  /* use the function */
  fmt.Println(getSquareRoot(9))
  /* create a slice of functions */
  funcArr := []func(float64) float64{
                  getSquareRoot,
                  getSquareRoot,
              }
  /* call every function */
  for i, funcVal := range funcArr {
    fmt.Printf("Calling function at index %d returns %.2f\n", i, funcVal(9))
  }
}

Output:

3
Calling function at index 0 returns 3.00
Calling function at index 1 returns 3.00

Function Closure

GoLang function can be nested and they have access to variables declared in the outer function.

package main
import "fmt"
func getSequence() func() int {
  i:=0
  return func() int {
      i+=1
      return i
    }
  }
func main(){
  /* nextNumber is now a function with i as 0 */
  nextNumber := getSequence()
  /* invoke nextNumber to increase i by 1 and return the same */
  fmt.Println(nextNumber())
  fmt.Println(nextNumber())
  fmt.Println(nextNumber())
}

Output:

1
2
3

Function Methods

GoLang does not have classes. However, you can define methods on types.

A method is a function with a special receiver argument.

The receiver appears in its own argument list between the func keyword and the method name.

In this example, the Abs method has a receiver of type Vertex named v.

package main
import (
"fmt"
"math"
)
type Vertex struct {
  X, Y float64
}
func (v Vertex) Abs() float64 {
  return math.Sqrt(v.X*v.X + v.Y*v.Y)
}
func main() {
  v := Vertex{3, 4}
  fmt.Println(v.Abs())
}

Output:

5