Adding to_string simplifies Elixir code development and debugging

Let's check on an example: we write a service with airports and directions.

defmodule Airport do
  defstruct [:id, :name]
end
defmodule Direction do
  defstruct [:origin, :destination]
  def example do
    madrid = %Airport{id: "MAD", name: "Madrid"}
    riga = %Airport{id: "RIX", name: "Riga"}
    %Direction{origin: riga, destination: madrid}
  end
end

So far, so good. Well, we ate a cookie, we look, what's next in fat. List of the most popular destinations?



First, make a small test list and get an unreadable sheet:

popular = Enum.map(1..5, fn _ -> Direction.example end)
# =>
# [%Direction{destination: %Airport{id: "MAD", name: "Madrid"},
#   origin: %Airport{id: "RIX", name: "Riga"}},
#  %Direction{destination: %Airport{id: "MAD", name: "Madrid"},
#   origin: %Airport{id: "RIX", name: "Riga"}},
#  %Direction{destination: %Airport{id: "MAD", name: "Madrid"},
#   origin: %Airport{id: "RIX", name: "Riga"}},
#  %Direction{destination: %Airport{id: "MAD", name: "Madrid"},
#   origin: %Airport{id: "RIX", name: "Riga"}},
#  %Direction{destination: %Airport{id: "MAD", name: "Madrid"},
#   origin: %Airport{id: "RIX", name: "Riga"}}]

Add a pinch of readability:

defimpl String.Chars, for: Airport do
  def to_string(airport) do
    "#{airport.name} (#{airport.id})"
  end
end
defimpl String.Chars, for: Direction do
  def to_string(direction) do
    "#{direction.origin} → #{direction.destination}"
  end
end

And we get a clear neat conclusion:

Enum.each(popular, fn(x) -> IO.puts(x) end)  
# =>
# Riga (RIX) → Madrid (MAD)
# Riga (RIX) → Madrid (MAD)
# Riga (RIX) → Madrid (MAD)
# Riga (RIX) → Madrid (MAD)
# Riga (RIX) → Madrid (MAD)

Now seriously

Sometimes during development you need to analyze the contents of variables. The internal representation is accurate, but not always readable. In such cases, you can teach Elixir to translate your structures into strings. To do this, define a function to_stringas part of the protocol implementation String.Chars.

As an added bonus, interpolation will automatically start working. Without an implementation to_stringfor airports, this would not work:

"#{direction.origin} → #{direction.destination}"

That's all. Readable code!