# TemplateParams

Runtime type-check for template preconditions, including instance variables
and local variables. Think of this as the method signature of a template.
There should be at least one of these assertions in almost every template.

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'template_params'
```

then run `bundle`.

## Usage

In rails, you may want a helper method like this:

```ruby
# app/helpers/application_helper.rb
require "template_params"
def template_param(*args, &block)
  ::TemplateParams::Assertion.assert(*args, &block)
end

# 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 }
```

## Development

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
[rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at
https://github.com/[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](contributor-covenant.org) code of conduct.

## License

The gem is available as open source under the terms of the [MIT
License](http://opensource.org/licenses/MIT).