Map.fetch

You're seeing just the function fetch, go back to Map module for more information.

fetch(map, key)

fetch(map(), key()) :: {:ok, value()} | :error

Fetches the value for a specific key in the given map.

If map contains the given key then its value is returned in the shape of {:ok, value}. If map doesn't contain key, :error is returned.

Inlined by the compiler.

iex> Map.fetch(%{a: 1}, :a)
{:ok, 1}
iex> Map.fetch(%{a: 1}, :b)
:error