Access protocol

Introduction #

The Access protocol is used by foo[bar] and also empowers the nested update functions in Kernel.

For instance, foo[bar] translates Access.get(foo, bar). Kernel.get_in/2, Kernel.put_in/3, Kernel.update_in/3 and Kernel.get_and_update_in/3 are also all powered by the Access protocol.

This protocol is implemented by default for keywords, maps and dictionary like types:

iex> keywords = [a: 1, b: 2]
iex> keywords[:a]
1

iex> map = %{a: 1, b: 2}
iex> map[:a]
1

iex> star_ratings = %{1.0 => "★", 1.5 => "★☆", 2.0 => "★★"}
iex> star_ratings[1.5]
"★☆"

The key comparison must be implemented using the === operator.

Source

Types #

t :: term

Functions #

get(container, key)

(function)

Specs

  • get(t, term) :: t

Accesses the given key in the container.

get_and_update(container, key, fun)

(function)

Specs

  • get_and_update(t, term, (term -> {get, term})) :: {get, t} when get: var

Gets a value and updates the given key in one pass.

The function must receive the value for the given key (or nil if the key doesn't exist in container) and the function must return a tuple containing the get value and the new value to be stored in the container.