TopolearnPointers decide whether a function sees a copy or the original, and they are central to methods.
A pointer holds the address of a value. &x takes the address of x, giving a *int if x is an int; *p reads or writes the value it points to. The zero value of a pointer is nil, and dereferencing nil panics.
Since Go passes everything by value, a function that must modify its argument takes a pointer:
func reset(n *int) { *n = 0 }
reset(&count)For structs, Go saves you the explicit dereference: if p is a *User, p.Name means (*p).Name. &User{Name: "Ann"} creates a struct and returns its address in one step, and new(T) allocates a zero T and returns *T.
It is completely safe to return a pointer to a local variable — the compiler notices the value outlives the function and allocates it on the heap. There's no manual memory management; the garbage collector frees values when nothing points to them.
Go has no pointer arithmetic (outside the unsafe package), which removes a whole class of memory bugs.
When to use a pointer:
- The callee must modify the value.
- The struct is large and copying it on every call would be wasteful.
- You need to represent "no value" with
nil.
Slices, maps, channels and functions already refer to shared data, so you rarely need a pointer to them. For small structs that are not modified, passing by value is simpler and often just as fast.
Example
package main
import "fmt"
type Account struct {
Owner string
Balance int
}
func deposit(a *Account, amount int) {
a.Balance += amount // same as (*a).Balance
}
func newAccount(owner string) *Account {
return &Account{Owner: owner} // safe: escapes to the heap
}
func main() {
acc := newAccount("ann")
deposit(acc, 50)
fmt.Println(acc.Balance) // 50
n := 10
p := &n
*p = 20
fmt.Println(n) // 20
}Remember
&xtakes an address,*pfollows it; zero value is nil- Pass a pointer when the callee must modify the value
- Returning a pointer to a local is safe; the GC manages memory
Watch out for
- Dereferencing a nil pointer (e.g. a field of a struct you never initialised).