Pointers #

// Go supports <em><a href="https://en.wikipedia.org/wiki/Pointer_(computer_programming)">pointers</a></em>,
// allowing you to pass references to values and records
// within your program.

package main

import "fmt"

// We'll show how pointers work in contrast to values with
// 2 functions: `zeroval` and `zeroptr`. `zeroval` has an
// `int` parameter, so arguments will be passed to it by
// value. `zeroval` will get a copy of `ival` distinct
// from the one in the calling function.
func zeroval(ival int) {
	ival = 0
}

// `zeroptr` in contrast has an `*int` parameter, meaning
// that it takes an `int` pointer. The `*iptr` code in the
// function body then _dereferences_ the pointer from its
// memory address to the current value at that address.
// Assigning a value to a dereferenced pointer changes the
// value at the referenced address.
func zeroptr(iptr *int) {
	*iptr = 0
}

func main() {
	i := 1
	fmt.Println("initial:", i)

	zeroval(i)
	fmt.Println("zeroval:", i)

	// The `&i` syntax gives the memory address of `i`,
	// i.e. a pointer to `i`.
	zeroptr(&i)
	fmt.Println("zeroptr:", i)

	// Pointers can be printed too.
	fmt.Println("pointer:", &i)
}

# `zeroval` doesn't change the `i` in `main`, but
# `zeroptr` does because it has a reference to
# the memory address for that variable.
$ go run pointers.go
initial: 1
zeroval: 1
zeroptr: 0
pointer: 0x42131100