Elixir Keyword Lists

Elixir Keyword Lists

Elixir Keyword Lists are a list of two item tuples where the first element of a tuple is an atom

iex(2)> k1 = [{:a, 1}, {:b, 2}, {:c, 3}, {:d, 4}]
[a: 1, b: 2, c: 3, d: 4]

iex(4)> k1 = [a: 1, b: 2, c: 3, d: 4] #a spoonful of sugar
[a: 1, b: 2, c: 3, d: 4]

iex(5)> k1 ++ {:b, 1} #not what we want
[{:a, 1}, {:b, 2}, {:c, 3}, {:d, 4} | {:b, 1}]

iex(6)> {:b, 1} ++ k1 #oops
** (ArgumentError) argument error
  :erlang.++({:b, 1}, [a: 1, b: 2, c: 3, d: 4])

iex(6)> k1 ++ [{:b, 1}] #remember the definition of keyword lists
[a: 1, b: 2, c: 3, d: 4, b: 1]

iex(7)> [{:b, 1}] ++ k1 #it works right
[b: 1, a: 1, b: 2, c: 3, d: 4]
  
iex(8)> k1 ++ [b: 1] #sugar is so sweet
[a: 1, b: 2, c: 3, d: 4, b: 1]

iex(9)> [b: 1] ++ k1 #sugar is so sweet 
[b: 1, a: 1, b: 2, c: 3, d: 4]

iex(24)> [a: 1] ++ {:b, 2} ++ [c: 3] #please don't do this
** (ArgumentError) argument error
    :erlang.++({:b, 2}, [c: 3])