What happens when you write to a nil map vs an empty map?

Writing to a nil map causes a runtime panic. Reading from a nil map returns the zero value safely. An empty map initialized with make() is safe for both reads and writes.

Nil map vs empty map

Best practices

1
Always initialize maps in struct constructors — do not rely on callers to initialize
2
Use make(map[K]V, hint) with a size hint when the approximate number of entries is known
3
Deleting from a nil map does NOT panic — delete() on nil map is a no-op
4
len() on a nil map returns 0 without panic
5
Range over a nil map produces zero iterations without panic