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 the receiver's state from within a method.

1type TreeNode struct {
2    Value int
3    Left  *TreeNode
4    Right *TreeNode
5}
6
7// Pointer receiver — modifies the tree
8func (n *TreeNode) Insert(val int) {
9    if val < n.Value {
10        if n.Left == nil {
11            n.Left = &TreeNode{Value: val}
12        } else {
13            n.Left.Insert(val)
14        }
15    } else {
16        if n.Right == nil {
17            n.Right = &TreeNode{Value: val}
18        } else {
19            n.Right.Insert(val)
20        }
21    }
22}

When to use:

• Pointer — mutation needed, large structs, implementing interfaces.
• Value — small structs, read-only methods, immutability desired.

Common mistakes:

• Mixing receiver types within one type — choose one for consistency.
• Value receiver on mutating method — silent bug.
• Nil pointer receiver dereference — method must check before accessing fields.
• Choosing value for a struct with embedded slices — the slice header copies but the underlying array shares.