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

Pointer receiver (*T) — method operates on the original value via pointer, can modify it, avoids copying large structs. Value receiver (T) — method operates on a copy, changes are discarded after the method returns.

The choice is fundamental to Go method design. Pointer receivers are the only way to mutate a receiver's fields from within a method. They also avoid the overhead of copying large structs.

1type Buffer struct {
2    data []byte
3}
4
5// Pointer receiver — modifies original
6func (b *Buffer) Write(p []byte) (int, error) {
7    b.data = append(b.data, p...)
8    return len(p), nil
9}
10
11// Value receiver — read-only, safe
12func (b Buffer) Len() int {
13    return len(b.data)
14}

Value receivers are appropriate for small, immutable types where copying is trivial and you want read-only semantics. They provide encapsulation by working on a snapshot.

1type Point struct{ X, Y float64 }
2
3func (p Point) DistanceTo(q Point) float64 {
4    dx := p.X - q.X
5    dy := p.Y - q.Y
6    return math.Sqrt(dx*dx + dy*dy)
7}

When to use:

• Pointer — when method mutates receiver, large structs (>2-3 fields), implementing interfaces with pointer receivers.
• Value — small structs (1-2 fields), read-only methods, immutable semantics desired.

Common mistakes:

• Mixing receiver types within one type — causes confusion about whether the type is pointer-ish or value-ish.
• Value receiver on a mutating method — silent data loss, changes are discarded.
• Nil pointer receiver dereference — method must check before accessing fields.
• Value receiver on a struct with embedded slices — copies the slice header but shares the underlying array.