/*
* Pointers and passing pointers in Go
* If you know C, it is very similar; but considerably cleaner
*
* @author gtowell
* Created: Aug 23, 2021
*/

package main

import "fmt"

func main() {
	a := 4  // store the value 4
	aa := &a // store the address (pointer) at which the 4 is stored

	fmt.Printf("%d %p\n", a,aa) // show the value and pointer
	a=126 // change 4 to 126
	fmt.Printf("%d %p\n", a,aa) // value changes, pointer does not

	var a3 *int // Like everthing else in Go, pointers have a "zero value"
	fmt.Printf("Uninitialized!! %p  %t\n", a3, (a3==nil))
	// This line does not work when immediately follow the pointer 
	// declaration.  Problem is that declaring pointer does not allocate space
	//*a3 = 55

	a3 = new(int)  // new returns a pointer to the specified type.  The space allocated gets the appropraite "zero" value
	fmt.Printf("Initialized!! %p  %t   %d\n", a3, (a3==nil), *a3)
	*a3 = 55

	pointerpass(a3)
	fmt.Printf("!! %p  %d\n", a3, *a3)


}

// can pass a pointer into a function.
// This then allows the function to chaneg the value stored at the pointer
// Why do this??
func pointerpass(aa3 *int) {
	fmt.Printf("Initialized!! %p  %d\n", aa3, *aa3)
	*aa3 = 42
}