go pointers: asterisks and ampersand reference

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)

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()
}