guard

Simple assertion macros to make code a little clearer.

Why? The static code analysis tool ameba has a rule called Style/GuardClause which is described as “Check for conditionals that can be replaced with guard clauses.” It’s a generally good idea; for example, instead of writing this:

def my_method
  if thing = @thing
    # use thing
  end
end

the tool recommends this:

def my_method
  return unless thing = @thing

  # use thing
end

which makes a lot of sense to me. However, at the time of this writing, the rule is disabled by default in ameba. I don't know why, but for me, I would disable it because having an assignment on the right of an inline conditional like that is hard to read—at least, I know it’s hard to read for me.

So I wrote guard which you use like this:

class MyClass
  include Guard
  def my_method
    thing = guard @thing

    # use thing
  end
end

That’s it—just put guard in front of the value in the assignment, and if the value is false or nil then the macro will return nil from the method immediately.

If instead you want to raise an exception, create an Exception in a block:

class MyClass
  include Guard
  def my_method
    thing = guard @thing { MyException.new %["oh bother," said Eeyore, "there is no thing there"] }

    # use thing
  end
end

And finally, if you only want to guard against nil values, but leave false alone, then you can use the guard! variants.

class MyClass
  include Guard

  @thing = false

  def my_method
    thing = guard! @thing

    # use thing, even if it’s `false`
  end
end

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     guard:
       github: plambert/guard.cr

2. Run shards install

Usage

require "guard"

class MyClass
  include Guard
end

Development

TODO: Write development instructions here

Contributing

1. Fork it (https://github.com/plambert/guard.cr/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Paul M. Lambert - creator and maintainer