Elixir Language Lists Keyword Lists
Example
Keyword lists are lists where each item in the list is a tuple of an atom followed by a value.
keyword_list = [{:a, 123}, {:b, 456}, {:c, 789}]
A shorthand notation for writing keyword lists is as follows:
keyword_list = [a: 123, b: 456, c: 789]
Keyword lists are useful for creating ordered key-value pair data structures, where multiple items can exist for a given key.
The first item in a keyword list for a given key can be obtained like so:
iex> keyword_list[:b]
456
A use case for keyword lists could be a sequence of named tasks to run:
defmodule TaskRunner do
def run_tasks(tasks) do
# Call a function for each item in the keyword list.
# Use pattern matching on each {:key, value} tuple in the keyword list
Enum.each(tasks, fn
{:delete, x} ->
IO.puts("Deleting record " <> to_string(x) <> "...")
{:add, value} ->
IO.puts("Adding record \"" <> value <> "\"...")
{:update, {x, value}} ->
IO.puts("Setting record " <> to_string(x) <> " to \"" <> value <> "\"...")
end)
end
end
This code can be called with a keyword list like so:
iex> tasks = [
...> add: "foo",
...> add: "bar",
...> add: "test",
...> delete: 2,
...> update: {1, "asdf"}
...> ]
iex> TaskRunner.run_tasks(tasks)
Adding record "foo"...
Adding record "bar"...
Adding record "test"...
Deleting record 2...
Setting record 1 to "asdf"...
