Atoms in

About Atoms

You can use atoms whenever you have a set of constants to express. Atoms provide a type-safe way to compare values. An atom is defined by its name, prefixed by a colon:

# Atoms start with a ':',
# followed by alphanumeric snake_cased characters
:an_atom

Many functions in Elixir's standard library return an atom to annotate the result:

Enum.fetch([1], 0)
# => {:ok, 1}
Enum.fetch([1], 2)
# => :error

Atoms are internally represented by an integer in a lookup table, which are set automatically. That makes comparing atoms faster than comparing strings. It is not possible to change this internal value. It is generally considered to be an anti-pattern to dynamically create atoms from user supplied input. The runtime only has space for a limited number of atoms, generating new atoms at runtime could fail if the atom table is full.