Isy

(pronounced like 'izzy')

Guard clauses for argument type assertions can be messy:

def fullname segments=[]
  raise ArgumentError, 'User#fullname expects 'segments' to be an Array' if segments.is_a? Array
  # ...
end

Setting aside that an issue of this type could be a sign of a greater architectural problem, Isy takes a declarative approach to solving the problem. Instead of dictating the contraints (and resulting response) to each argument type, you can leverage Isy's simple interface:

The primary use of Isy is through the isy method, which is included into Object upon initialization

You can call isy from any point, but it's intended use is to be treated like a "guard clause" to assert method argument types before those arguments are used (and potentially wreak havoc throughout the implementation:

def fullname segments=[]
  isy segments, Array
  # ...
end

The first argument is the subject of the test (i.e. what should match the proceeding assertion) The second argument is the class, Range, Regexp or any object (type) which responds to ===.

If the subject doesn't match the provided type, then it raises a formatted exception describing what argument value was a type mismatch (as an Isy::ArgumentTypeMismatch exception).

Alternatively, you can use the predicate version for type assertion:

def fullname segments=[]
  if isy? segments, Array
    # passes
  end
end

In the previous example, the interface is the same: subject, arguments, optional block. The difference is that if the assertion fails, it will catch the Isy::ArgumentTypeMismatch exception and return false.

Optionally, in place of a type as the second argument, you can pass a block, and perform a more complex comparison operation:

def fullname segments
  isy segments { |seg| seg.length == 3 }
  # ...
end

As illustrated above, isy yields to the operation the first argument (segments). The expectation is that the value returned by the operation (block) is a boolen (true => passes, false => failed).

Note: predicate version has the same support

It's not great against a more "native" implementation; but, where you lose a little in performance, you (may) gain in an ability to quickly reason about the code.

A native implementation is incredibly light (see above): no additional dependencies and logistical overhead. Using Isy you're introducing an additional dependency and better support for evaluation routines (by providing a block).

To run a comparison benchmark:

$ ruby spec/benchmark.rb

Add this line to your application's Gemfile:

gem 'isy'

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/isy. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

Authored by the Engineering Team of Coding ZEAL

Copyright (c) 2017 Zeal, LLC. Licensed under the MIT license.