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

Pointer receiver — the method receives *T, can modify the original value, avoids copying. Value receiver — the method receives T, works on a copy, cannot affect the original.

The choice affects mutability, performance, and interface satisfaction. If you define even one method with a pointer receiver, Go encourages (but doesn't enforce) making all methods on that type use pointer receivers for consistency.

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

Performance consideration: Value receivers copy the entire struct. For small structs (one or two fields) this is negligible. For large structs (embedded slices, maps, many fields), pointer receivers avoid the copy.

When to use:

• Pointer — when the method mutates the receiver, or the struct is large.
• Value — when the method is read-only and the struct is small.

Common mistakes:

• Mixing receiver types within one type — leads to confusion about whether a type is "pointer-ish" or "value-ish".
• Using a value receiver on a method that needs to modify the struct — silent data loss.
• Passing a value type to an interface that expects a pointer receiver method — the value won't satisfy the interface.
• Forgetting that methods with value receivers don't work well with nil receivers (they receive a copy of nil, which can still dereference fields if they are pointers).