---

name: go-nil-map description: Map nil safety - read OK, write panics

Map Nil Safety

Problem

Reading from nil map returns zero value. Writing to nil map panics.

Pattern

WRONG - Write to nil map

Copyvar m map[string]int  // nil map
m["key"] = 42         // PANIC: assignment to entry in nil map

CORRECT - Initialize with make

Copym := make(map[string]int)
m["key"] = 42  // OK

Reading is Safe

Copyvar m map[string]int  // nil map
v := m["key"]         // OK, v = 0 (zero value)
v, ok := m["key"]     // OK, v = 0, ok = false

Quick Fix

• Always initialize maps with make() before writing
• Check if map is nil before range/write
• Reading from nil map is safe but returns zero values

Defensive Pattern

Copyif m == nil {
    m = make(map[string]int)
}
m["key"] = 42