Programming Elixir ≥ 1.6

Pattern Matching and Updating Maps

The question we most often ask of our maps is, “Do you have the following keys (and maybe values)?” For example, given this map:

person = %{ name: "Dave", height: 1.88 }

• Is there an entry with the key :name?

  iex> %{ name: a_name } = person
  %{height: 1.88, name: "Dave"}
  iex> a_name
  "Dave"

• Are there entries for the keys :name and :height?

  iex> %{ name: _, height: _ } = person
  %{height: 1.88, name: "Dave"}

• Does the entry with key :name have the value "Dave"?

  iex> %{ name: "Dave" } = person
  %{height: 1.88, name: "Dave"}

Our map does not have the key :weight, so the following pattern match fails:

iex> %{ name: _, weight: _ } = person
** (MatchError) no match of right ...