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

Pointer receiver (*T) — operates on the original value, can modify it. Value receiver (T) — operates on a copy, modifications are discarded.

When you declare a method with a pointer receiver, the method gets a pointer to the receiver. Any changes to the receiver's fields persist after the method returns. Value receivers get a snapshot — the caller never sees changes.

1type BankAccount struct {
2    balance float64
3}
4
5// Pointer receiver — mutates original
6func (a *BankAccount) Deposit(amount float64) {
7    a.balance += amount
8}
9
10// Value receiver — read-only, safe
11func (a BankAccount) Balance() float64 {
12    return a.balance
13}
14
15acct := BankAccount{balance: 100}
16acct.Deposit(50)
17fmt.Println(acct.Balance())  // 150

When to use:

• Pointer — when the method needs to modify the receiver, or the struct is large and copying is expensive.
• Value — when the method is read-only and the struct is small (a few fields).

Common mistakes:

• Mixing receiver types across methods of the same type — Go recommends consistency (all pointer or all value).
• Using a value receiver when you need to modify the struct — silent bug, changes are lost.
• Forgetting that interfaces always use pointer semantics: if you have a value v and call an interface method on &v, you must pass &v, not v.
• Large struct with value receiver causing performance issues from repeated copying.