Access.at

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

Specs

at(integer()) :: access_fun(data :: list(), current_value :: term())

Returns a function that accesses the element at index (zero based) of a list.

The returned function is typically passed as an accessor to Kernel.get_in/2, Kernel.get_and_update_in/3, and friends.

Examples

iex> list = [%{name: "john"}, %{name: "mary"}]
iex> get_in(list, [Access.at(1), :name])
"mary"
iex> get_in(list, [Access.at(-1), :name])
"mary"
iex> get_and_update_in(list, [Access.at(0), :name], fn prev ->
...>   {prev, String.upcase(prev)}
...> end)
{"john", [%{name: "JOHN"}, %{name: "mary"}]}
iex> get_and_update_in(list, [Access.at(-1), :name], fn prev ->
...>   {prev, String.upcase(prev)}
...> end)
{"mary", [%{name: "john"}, %{name: "MARY"}]}

at/1 can also be used to pop elements out of a list or a key inside of a list:

iex> list = [%{name: "john"}, %{name: "mary"}]
iex> pop_in(list, [Access.at(0)])
{%{name: "john"}, [%{name: "mary"}]}
iex> pop_in(list, [Access.at(0), :name])
{"john", [%{}, %{name: "mary"}]}

When the index is out of bounds, nil is returned and the update function is never called:

iex> list = [%{name: "john"}, %{name: "mary"}]
iex> get_in(list, [Access.at(10), :name])
nil
iex> get_and_update_in(list, [Access.at(10), :name], fn prev ->
...>   {prev, String.upcase(prev)}
...> end)
{nil, [%{name: "john"}, %{name: "mary"}]}

An error is raised if the accessed structure is not a list:

iex> get_in(%{}, [Access.at(1)])
** (RuntimeError) Access.at/1 expected a list, got: %{}