Errors in

About Errors

While Elixir programmers often say "let it crash" and code for the "happy path", there are often times we need to rescue the function call to return a specific value, message or release system resources.

• Functions that raise errors under normal circumstances should have ! at the end of their name.

• Functions may alternatively return atoms and tuples to indicate success and failure:

  Map.fetch(%{a: 1}, :a)
  # => {:ok, 1}
  Map.fetch(%{a: 1}, :b)
  # => :error
  
  Map.fetch!(%{a: 1}, :b)
  # => raises KeyError
  

Avoid anti-patterns

Avoid programming patterns that use errors to control logical flow. This is an anti-pattern in Elixir.

# Avoid using errors for control-flow.
try do
  {:ok, value} = MyModule.janky_function()
  "All good! #{value}."
rescue
  e in RuntimeError ->
    reason = e.message
    "Uh oh! #{reason}."
end

# Rather, use control-flow structures for control-flow.
case MyModule.janky_function() do
  {:ok, value} -> "All good! #{value}."
  {:error, reason} -> "Uh oh! #{reason}."
end