Parameter assertions for your ruby view templates
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Latest commit a4f300c Oct 10, 2016 @jaredbeck Release 0.1.1
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Runtime type-check for template preconditions, including instance variables and local variables. Think of this as the method signature of a template, as the documentation.


  1. Add it to your Gemfile and run bundle.

    gem 'template_params'
  2. If you're using rails, add a helper method.

    # app/helpers/application_helper.rb
    def template_param(*args, &block)
     ::TemplateParams::Assertion.assert(*args, &block)

    If you're not using rails, let me know how you install it, and I'll put that here.


# Assert `poll` is defined. If not, raises an `ArgumentError` (the "arguments"
# of the template are invalid).
template_param { poll }

# Assert `@course` is defined. Meaningless because instance variables are
# always defined.
template_param { @course }

# Assert `poll.is_a?(::Poll)`. If not, raises a `TypeError`.
template_param(::Poll) { poll }

# Assert `@course.is_a?(::Course)`
template_param(::Course) { @course }

# Assert `@course` is either a `::Course` or `nil`
template_param(::Course, allow_nil: true) { @course }


After checking out the repo, run bin/setup to install dependencies. Then, run bundle exec rspec 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


Bug reports and pull requests are welcome on GitHub at[USERNAME]/template_assertions. 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.


The gem is available as open source under the terms of the MIT License.