Functions and Methods

Anonymous Functions

Anonymous functions can be stored in variables and use surrounding values.

closure An anonymous function can close over variables from the surrounding function.

Anonymous Functions

multiplier
anonymous_functions.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var multiplier = 2
	scale := func(value int) int {
		return value * multiplier
	}
	result := scale(4)

	fmt.Println("multiplier=", multiplier)
	fmt.Println("result=", result)
}

package main

import "fmt"

func main() {
	var multiplier = 3
	scale := func(value int) int {
		return value * multiplier
	}
	result := scale(4)

	fmt.Println("multiplier=", multiplier)
	fmt.Println("result=", result)
}

package main

import "fmt"

func main() {
	var multiplier = 5
	scale := func(value int) int {
		return value * multiplier
	}
	result := scale(4)

	fmt.Println("multiplier=", multiplier)
	fmt.Println("result=", result)
}

  1. multiplier ← 2, scale ← (func(int) int)(⟨addr A⟩)

    5func main() {6  var multiplier→ 2 = 2 //@multiplier=3, 57  scale→ (func(int) int)(⟨addr A⟩) := func(value int) int {8    return value * multiplier9  }10  result := scale(4)

  2. func(value int) int

    6var multiplier = 2 //@multiplier=3, 57scale := func(value4 int) int {8  return value4 * multiplier29}

  3. result ← 8

    9  }10  result→ 8 := scale(4)1112  fmt.Println("multiplier=", multiplier2)13  fmt.Println("result=", result8)14}
    outputmultiplier= 2
result= 8

  1. multiplier ← 3, scale ← (func(int) int)(⟨addr A⟩)

    5func main() {6  var multiplier→ 3 = 37  scale→ (func(int) int)(⟨addr A⟩) := func(value int) int {8    return value * multiplier9  }10  result := scale(4)

  2. func(value int) int

    6var multiplier = 37scale := func(value4 int) int {8  return value4 * multiplier39}

  3. result ← 12

    9  }10  result→ 12 := scale(4)1112  fmt.Println("multiplier=", multiplier3)13  fmt.Println("result=", result12)14}
    outputmultiplier= 3
result= 12

  1. multiplier ← 5, scale ← (func(int) int)(⟨addr A⟩)

    5func main() {6  var multiplier→ 5 = 57  scale→ (func(int) int)(⟨addr A⟩) := func(value int) int {8    return value * multiplier9  }10  result := scale(4)

  2. func(value int) int

    6var multiplier = 57scale := func(value4 int) int {8  return value4 * multiplier59}

  3. result ← 20

    9  }10  result→ 20 := scale(4)1112  fmt.Println("multiplier=", multiplier5)13  fmt.Println("result=", result20)14}
    outputmultiplier= 5
result= 20

Follow the Closure

  1. multiplier starts as 2.
  2. scale is an anonymous function stored in a variable.
  3. The function reads the surrounding multiplier.
  4. scale(4) calculates 4 * 2.
  5. The program prints multiplier= 2 and result= 8. | multiplier | call | result | | --- | --- | --- | | 2 | scale(4) | 8 | | 3 | scale(4) | 12 | | 5 | scale(4) | 20 |

Exercise: anonymous_functions.go

Reproduce multiplier= 2 and result= 8, then use the pinned multiplier variants 3 and 5 to predict result= 12 and result= 20.