Go: What is the difference between pointer and value receiver?

Pointer receiver (*T) — method gets a pointer to the value, can modify the original, avoids copying. Value receiver (T) — method gets a copy, changes don't affect the original.

The receiver type determines whether the method has side effects. Pointer receivers are the only way to mutate a receiver's state from within a method.

1type Counter struct {
2    count int
3}
4
5// Pointer receiver — can modify
6func (c *Counter) Increment() {
7    c.count++  // modifies original
8}
9
10// Value receiver — read-only
11func (c Counter) Value() int {
12    return c.count
13}
14
15var c Counter
16c.Increment()
17c.Increment()
18fmt.Println(c.Value())  // 2

Performance consideration: Value receivers copy the entire struct. For small structs this is negligible. For large structs, pointer receivers avoid the copy.

When to use:

• Pointer — method mutates receiver, large structs, interface implementation.
• Value — small structs, read-only methods, immutable semantics.

Common mistakes:

• Mixing receiver types within one type — leads to confusion.
• Value receiver on a mutating method — silent data loss.
• Nil pointer receiver dereference — must check before accessing fields.
• Value receiver on a struct with slices — copies the header but shares the array.