Maps

These are key-value stores.

Keyword lists allow only atom-keys and are ordered.

But Maps do not.

map = %{ph -> manila, us -> wash}

Setting

m = %{a: 1}

m = %{a => 1} # the => goes deeper

%{a: 1} == %{:a => 1}

map = %{:atom => "string", "string" => "string"}
mapshortcut = %{atom: "string", atom2: "string"}

# binding to variable
%{"string" => string}

defstruct [:name, :age]

attributes_map = %{name: "Lam", age: 20}
struct()

Calling

m[:a]
1

map.atom
map["string"]
map[:atom]

Vars can be set as map keys

v = "very long name representing a long integer"
m = %{v: 123456789}
m = %{v => 123456789} # want to assign what v represents and attach it to 123456789 value

If a duplicate is added to a map, it will replace the former value:

m = %{:v => 1, :v => 2}
%{v: 2}

m = %{v: 1, v: 2}
%{v: 2}

Updating Maps via Pattern Matching

Unlike other languages where = forces assignment, = in Elixir is a query for match.

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


%{ name: a_name } = person  # checks if person has a name key
%{height: 1.88, name: "Dave"} 

%{ name: _, height: _ } = person  # checks if there are values for the keys :name and :height
%{height: 1.88, name: "Dave"}

%{ name: "Dave" } = person # checks whether the key :name has the value "Dave"

%{ name: _, weight: _ } = person # check for key :weight
** (MatchError) no match of right hand side value: %{height: 1.88, name: "Dave"}

Updating a map ceates a new map

m = %{a: 1}
m = %{m | a: 2} # or m = %{m | a => 2}