Go — Pointers

What is a pointer

package main

import "fmt"

func main() {
    x := 10
    p := &x    // p is *int

    fmt.Println(*p)  // 10 (dereference)
    *p = 20
    fmt.Println(x)   // 20
}

Pointer types

var p *int       // nil pointer
var s *string    // nil pointer

x := 42
p = &x           // points to x

Passing by value vs pointer

func byValue(x int) {
    x = 100 // Only changes local copy
}

func byPointer(x *int) {
    *x = 100 // Changes the original
}

func main() {
    a := 5
    byValue(a)
    fmt.Println(a) // 5

    byPointer(&a)
    fmt.Println(a) // 100
}

New and make

// new: allocates memory, returns pointer
p := new(int)
fmt.Println(*p) // 0

// make: initializes slices, maps, channels
s := make([]int, 5)
m := make(map[string]int)
ch := make(chan int)

Nil pointers

var p *int
fmt.Println(p == nil) // true

// Dereferencing nil causes panic
// fmt.Println(*p) // PANIC!

Best practices

• Use pointers for large structs to avoid copying
• Use pointers when you need to modify the original
• Return errors instead of nil pointers
• Use new for single allocations, make for slices/maps/channels

Mini Practice

Write Go code that:

1. Swaps two integers using pointers
2. Uses new to allocate a struct
3. Demonstrates pass-by-value vs pass-by-pointer
4. Shows nil pointer checking

Up Next

In the next lesson, you'll learn about Methods — functions on types.