Pointers

Pointers in Go allow you to reference a variable's memory address so you can directly access and modify the value stored at that location.

&: Get the memory address of a variable.
*: Access or modify the value stored at a pointer's address.

func main() {
	// Declaring a variable:
	a := 10

	fmt.Println(a)        // 10
	fmt.Printf("%T\n", a) // int

	// Declaring a pointer and assigning it the address of 'a':
	ptr := &a

	fmt.Println(ptr)        // 0xc0000a4010 (memory address of 'a')
	fmt.Printf("%T\n", ptr) // *int
	fmt.Println(*ptr)       // 10 (value at the memory address)

	// Changing the value at the memory address:
	*ptr = 20

	fmt.Println(a) // 20
}

By using pointers as function parameters, you pass the memory address of a variable rather than a copy of its value. This changes Go's default pass-by-value behavior and allows the function to modify the original data directly.
func main() {
	num := 10
	fmt.Println(num) // 10

	resetVal(num)
	fmt.Println(num) // 10

	resetPtr(&num)
	fmt.Println(num) // 0
}

func resetVal(val int) {
	val = 0
}

func resetPtr(val *int) {
	*val = 0
}

Pointers as function parameters also allow you to work with large data structures more efficiently.

No unnecessary copying = Better performance.

Without pointer:

func main() {
	arr := [5]int{1, 2, 3, 4, 5}

	fmt.Printf("mem addr (arr): %p, arr: %v\n", &arr, arr) // mem addr (arr): 0xc00011e000, arr: [1 2 3 4 5]
	myFunc(arr) // mem addr (items): 0xc00011e060, items: [1 2 3 4 5]
}

func myFunc(items [5]int) [5]int {
	fmt.Printf("mem addr (items): %p, items: %v\n", &items, items)
	return items
}

With pointer:

func main() {
	arr := [5]int{1, 2, 3, 4, 5}

	fmt.Printf("mem addr (arr): %p, arr: %v\n", &arr, arr) // mem addr (arr): 0xc00011e000, arr: [1 2 3 4 5]
	myFunc(&arr) // mem addr (items): 0xc00011e000, items: [1 2 3 4 5]
}

func myFunc(items *[5]int) [5]int {
	fmt.Printf("mem addr (items): %p, items: %v\n", items, *items)
	return *items
}

Since arrays are fully independent pass-by-value types in Go (like booleans, numerics, and structs), passing them normally creates a full copy. Using pointers avoids that copying.