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

Pointer receiver (*T) — operates on the original via pointer, can modify it, avoids copying. Value receiver (T) — operates on a copy, changes don't affect the original.

The choice is fundamental: pointer receivers allow mutation and avoid copy overhead, while value receivers provide encapsulation by working on a snapshot.

1type Config struct {
2    data map[string]string
3}
4
5// Pointer receiver — modifies original
6func (c *Config) Set(key, val string) {
7    c.data[key] = val
8}
9
10// Value receiver — safe read
11func (c Config) Get(key string) string {
12    return c.data[key]
13}
14
15cfg := Config{data: make(map[string]string)}
16cfg.Set("host", "localhost")
17fmt.Println(cfg.Get("host"))  // localhost

When to use:

• Pointer — mutation needed, large structs, interface implementation.
• Value — small structs, read-only, immutability.

Common mistakes:

• Mixing receiver types — inconsistent behavior.
• Value receiver for mutating method — silent data loss.
• Nil pointer dereference — must check before accessing fields.
• Value on struct with slices — copies header, shares backing array.