Pointer Receiver Nil

Problem

Methods with pointer receivers can be called on nil. Must handle nil receiver.

Pattern

WRONG - Assume receiver is non-nil

type Tree struct {
    Value int
    Left  *Tree
}

func (t *Tree) Sum() int {
    return t.Value + t.Left.Sum()  // PANIC if t or t.Left is nil
}

CORRECT - Handle nil receiver

type Tree struct {
    Value int
    Left  *Tree
    Right *Tree
}

func (t *Tree) Sum() int {
    if t == nil {
        return 0  // Nil tree has sum of 0
    }
    return t.Value + t.Left.Sum() + t.Right.Sum()
}

// Now safe to call
var tree *Tree  // nil
sum := tree.Sum()  // Returns 0, no panic

Use Cases

Nil receiver pattern enables elegant recursive algorithms and optional behavior.

Quick Fix

• Check if receiver is nil at method start
• Define sensible zero behavior for nil receiver
• Document whether methods are nil-safe

When NOT to Use

If nil receiver doesn't make semantic sense, panic early with clear message.