From: Per-erik Martin <lists@...>
Date: 2013-06-12T17:23:43+09:00
Subject: Re: How would I refactor these four `unless` statements?

Rafal C. wrote in post #1112088:
> Let's say I have the following four `unless` statements in a row. At
> first I thought about using `if` and `elsif` statements and negate the
> condition but I'm not sure which way is suitable/readable/good-practice.
>
>   unless @params.include?(:js_code) || @params.include?(:code_url)
>     raise BadParameters, 'You must include at least one...'
>   end
>   unless @params.include?(:compilation_level)
>     raise BadParameters, 'The :compilation_level...'
>   end
>   unless @params.include?(:output_format)
>     raise BadParameters, 'The :output_format...'
>   end
>   unless @params.include?(:output_info)
>     raise BadParameters, 'The :output_info...'
>   end
>
> Thanks in advance!

I think they're fine. When it comes to logical statements for error
handling, keeping it simple, systematic, and easy to understand is a
good thing. Building some larger, more complex expressions just to make
the code shorter will only obfuscate it and require a reader to do more
interpretation in the head to make sense of it.
Possibly, you can define a helper method for the simple cases like this:

def required(name, message)
  unless @params.include?(name)
    raise BadParameters, message
  end
end

and turn three of them into:

required(:compilation_level, 'The :compilation_level...')
required(:output_format, 'The :output_format...')
required(:output_info, 'The :output_info...')

If the messages are completely uniform (except for the parameter name of
course), you can also do it this way:

def required(names)
  names.each do |name|
    unless @params.include?(name)
      raise BadParameters, "The #{name} ..."
    end
  end
end

required([:compilation_level, :output_format, :output_info])

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