Avoid the use of unless conditional with an else clause in Ruby

In Ruby, there are three ways of negating conditions. The first one is the not keyword. The second one is with the negating ! (the bang operator of negation). The third and more natural sounding way of negating is the unless keyword. The keyword unless, express the exact same semantics as if not (expression) and if !(expression).

So we can summarise the three negating conditions in the following gist:

unless (x == 0) the same as if not (x == 0) the same as if !(x == 0)

By using unless in our code we aim to provide better readability and a more natural sounding in the English of the code. Think about it, unless sounds clearer than if not and it's much more easy to understand the logic in the part of code that is involved. Furthermore, Ruby language, allows the use of unless with an else clause like in the following gist:

unless (x == 0)
  puts "Not a Zero"
else
  puts "A Zero"
end

The above is a valid example of code that will be parsed without errors or warnings. However, is hard to follow the logic even in the above simple example. In general, if/else reads much better than unless/else. The use of unless with an else clause is considered a bad practice and should be avoided. By flipping around the logic of the conditional statement above and by replacing the former with the latter statement, we result in a statement with the exact same conditional meaning.

if (x == 0)
  puts "A Zero"
else
  puts "Not a Zero"
end

Note: We also avoided to use the other negating conditionals and just flip the statement to an if/else that is easier to understand by every member of the team. To summarize unless sounds better and it is used widely as a single conditional modifier. If there is the need of an else clause, you should refactor to an if/else statement.