credo_results

A library adding credo checks to deal with :ok/:error results (:ok, :error, {:ok, ...}, {:error, ...})

Currently there are two different checks implemented:

CredoResults.ConsistentResultCheck

This rule works under the assumption that a function should either always return an :ok/:error result, or never return an :ok/:error result. This is because a function either has the possibility of failure (meaning the caller will need to deal with it) or it doesn't. If a function has the possibility of failure, it should always be clear if it's succeeding (an :ok result) or failing (an :error result)

Some examples that would be flagged by this check:

• A function sometimes returns an integer and sometimes returns :error (whereas it would be better to return {:ok, integer()})
• A function sometimes returns {:ok, String.t()} and sometimes returns nil (whereas it would be better to return :error instead of nil)
• A function sometimes returns {:ok, map()} and sometimes returns :not_found (whereas it would be better to return {:error, :not_found} instead of :not_found)

CredoResults.TwoElementCheck

This simply checks for any usage in your project of {:ok, ...} or {:error, ...} tuples which have three elements or more (a three elements tuple being the :ok/:error atom plus two values).

The idea here is that you should avoid using tuples larger than two elements because :ok/:error tuples are returned up a stack and get combined with other :ok/:error results, and having multiple patterns to match is painful.

Installation

If available in Hex, the package can be installed by adding credo_result_types to your list of dependencies in mix.exs:

def deps do
  [
    {:credo_result_types, "~> 0.1.0"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/credo_result_types.