Golang - Asterisk and Ampersand Cheatsheet

values_pointers.go

/*
********************************************************************************
Golang - Asterisk and Ampersand Cheatsheet
********************************************************************************

Also available at: https://play.golang.org/p/lNpnS9j1ma

Allowed:
--------
p := Person{"Steve", 28} 	stores the value
p := &Person{"Steve", 28} 	stores the pointer address (reference)
PrintPerson(p) 			passes either the value or pointer address (reference)
PrintPerson(*p) 		passes the value
PrintPerson(&p) 		passes the pointer address (reference)
func PrintPerson(p Person)	ONLY receives the value
func PrintPerson(p *Person)	ONLY receives the pointer address (reference)

Not Allowed:
--------
p := *Person{"Steve", 28} 	illegal
func PrintPerson(p &Person)	illegal

*/

package main

import (
	"fmt"
)

type Person struct {
	Name string
	Age int
}

// This only works with *Person, does not work with Person
// Only works with Test 2 and Test 3
func (p *Person) String() string {
	return fmt.Sprintf("%s is %d", p.Name, p.Age)
}

// This works with both *Person and Person, BUT you can't modiy the value and
// it takes up more space
// Works with Test 1, Test 2, Test 3, and Test 4
/*func (p Person) String() string {
	return fmt.Sprintf("%s is %d", p.Name, p.Age)
}*/

// *****************************************************************************
// Test 1 - Pass by Value
// *****************************************************************************

func test1() {
	p := Person{"Steve", 28}
	printPerson1(p)
	updatePerson1(p)
	printPerson1(p)
}

func updatePerson1(p Person) {
	p.Age = 32
	printPerson1(p)
}

func printPerson1(p Person) {
	fmt.Printf("String: %v | Name: %v | Age: %d\n",
        p,
        p.Name,
        p.Age)
}

// *****************************************************************************
// Test 2 - Pass by Reference
// *****************************************************************************

func test2() {
	p := &Person{"Steve", 28}
	printPerson2(p)
	updatePerson2(p)
	printPerson2(p)
}

func updatePerson2(p *Person) {
	p.Age = 32
	printPerson2(p)
}

func printPerson2(p *Person) {
	fmt.Printf("String: %v | Name: %v | Age: %d\n",
        p,
        p.Name,
        p.Age)
}

// *****************************************************************************
// Test 3 - Pass by Reference (requires more typing)
// *****************************************************************************

func test3() {
	p := Person{"Steve", 28}
	printPerson3(&p)
	updatePerson3(&p)
	printPerson3(&p)
}

func updatePerson3(p *Person) {
	p.Age = 32
	printPerson3(p)
}

func printPerson3(p *Person) {
	fmt.Printf("String: %v | Name: %v | Age: %d\n",
        p,
        p.Name,
        p.Age)
}

// *****************************************************************************
// Test 4 - Pass by Value (requires more typing)
// *****************************************************************************

func test4() {
	p := &Person{"Steve", 28}
	printPerson4(*p)
	updatePerson4(*p)
	printPerson4(*p)
}

func updatePerson4(p Person) {
	p.Age = 32
	printPerson4(p)
}

func printPerson4(p Person) {
	fmt.Printf("String: %v | Name: %v | Age: %d\n",
        p,
        p.Name,
        p.Age)
}

// *****************************************************************************
// Main
// *****************************************************************************

/*
Outputs:
String: {Steve 28} | Name: Steve | Age: 28
String: {Steve 32} | Name: Steve | Age: 32
String: {Steve 28} | Name: Steve | Age: 28
String: Steve is 28 | Name: Steve | Age: 28
String: Steve is 32 | Name: Steve | Age: 32
String: Steve is 32 | Name: Steve | Age: 32
String: Steve is 28 | Name: Steve | Age: 28
String: Steve is 32 | Name: Steve | Age: 32
String: Steve is 32 | Name: Steve | Age: 32
String: {Steve 28} | Name: Steve | Age: 28
String: {Steve 32} | Name: Steve | Age: 32
String: {Steve 28} | Name: Steve | Age: 28
*/
func main() {	
	test1()
	test2()
	test3()
	test4()
}

Thanks!

thx

Good stuff.

Thank you!

Awesome!

Thank you!

Thank you!

Just to clarify, in line 43 "it takes up more space" means calling a method like this during runtime uses more memory?

@erpel nah, it just requires more characters to type.

awsome !!!

easy to understand, thanks!

This is probably the best explanation on this topic on the internet

This is probably the best explanation on this topic on the internet

@stankud Wonderful to hear, thanks!

Thanks!

I was in doubt about the asterisk at function's parameters. Simple and direct explanation, thanks!