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Elixir Tips and Idioms

Maps

to get a value from a nested map, use the h Kernel.get_in() function

iex(1)> h Kernel.get_in

iex(2)> maps_in_map = 
iex(...)> %{uno: %{dos: %{tres: "loco"}}}

iex(3)> get_in(
iex(...)> maps_in_map, 
iex(...)> [:uno, :dos, :tres]
iex(...)>)
# => "loco"

Structs

to get a value from a struct, use the . syntax. note, Access protocol %SomeStruct{mood: “happy”}[:mood] does not work on structs

# define a struct
defmodule SomeStruct do
  defstruct mood: nil
end

"happy" = %SomeStruct{mood: "happy"}.mood
# => "happy"

# under the hood, a struct is just a Map 
# with the special __struct__ attribute
%SomeStruct{}.__struct__
# => SomeStruct

# so, except for the Access protocol, 
# we could also use the Map functions
"happy" = Map.get(%SomeStruct{mood: "happy"}, :mood)
# => "happy"

# but the best way to extract a value from a 
# struct, ...pattern match
%{mood: mood} = %SomeStruct{mood: "happy"}
# mood => "happy"
%SomeStruct{mood: mood} = %SomeStruct{mood: "happy"}
# mood => "happy

IEx

example default config in iex.exs

IEx.configure(
  colors: [
    enabled: true,
    eval_result: [:light_green],
    eval_error: [:light_magenta],
    stack_info: [:light_blue]
  ],
  default_prompt:
    [
      # a neon purple
      "\r\e[38;5;129m",
      # IEx context
      "%prefix",
      # forest green expression count
      "\e[38;5;112m(%counter)",
      # neon purple ">"
      "\e[38;5;129m>",
      # and reset to default color
      "\e[0m"
    ]
    |> IO.chardata_to_string()
)

note: default_prompt uses IO.ANSI color codes