# Usable [![Gem Version](https://badge.fury.io/rb/usable.svg)](http://badge.fury.io/rb/usable) [![Build Status](https://travis-ci.org/ridiculous/usable.svg)](https://travis-ci.org/ridiculous/usable) [![Code Climate](https://codeclimate.com/github/ridiculous/usable/badges/gpa.svg)](https://codeclimate.com/github/ridiculous/usable)

An elegant way to mount and configure your modules. Usable gives you control over which methods are included, and a simple
interface to help you call dynamic methods with confidence.

```ruby
module VersionMixin
  def save_version
    "Saving up to #{self.class.usable_config.max_versions} versions to #{self.class.usable_config.table_name}"
  end

  def destroy_version
    "Deleting versions from #{self.class.usable_config.table_name}"
  end
end

class Model
  extend Usable

  usable VersionMixin, only: :save_version do |config|
    config.max_versions = 10
    config.table_name = 'custom_versions'
  end

  def save
    self.class.usable_method(self, :save_version).call
  end
end

model = Model.new
model.save_version     # => "Saving up to 10 versions to custom_versions"
model.destroy_version  # => NoMethodError: undefined method `destroy_version' for #<Model:...
```
`Model` now has a `#save_versions` method but no `#destroy_version` method. Usable has effectively mixed in the given module
using `include`. Ruby 2+ offers the `prepend` method, which can be used instead by specifying it as the `:method` option:

```ruby
Model.usable VersionMixin, method: :prepend
```

Usable reserves the `:only` and `:method` keys. All other keys in the given hash are defined as config settings. 
If you really want to define a config on the target class with one of these names, you can simply define them in the block:

```ruby
Model.usable VersionMixin, only: [:save_version] do |config|
  config.only = "Will be set on `Model.usable_config.only`"
end
```

## Confidently calling methods

We should all be writing [confident code](http://www.confidentruby.com/), which is why you might want to call configurable
methods through the `usable_method` class level function. Methods passed in with the `:only` option
will _always_ return `nil` when called. Thus, the confidence.

Here's the same example as above, rewritten to call methods through the Usable interface:

```ruby
Model.usable_method(model, :save_version).call    # => "Saving up to 10 versions to custom_versions"
Model.usable_method(model, :destroy_version).call # => nil
```

## Separate the _included_ module from the _configurable_ methods

Sometimes you want to define methods on a module and have them always be included. To do this, define a module named 
`UsableSpec` in the scope of the module you are mounting. `Usable` will detect this and use he "spec" module to configure 
the available methods. Any naming conflicts will be resolved by giving precedence to the parent module.

For example:

```ruby
module Mixin
  def name
    "defined by Mixin"
  end

  def from_mixin
    "always here"
  end

  # @description Usable will apply the :only option to just the methods defined by this module
  module UsableSpec
    def from_spec
      "can be excluded"
    end

    def name
      "defined by UsableSpec"
    end
  end
end

class Example
  extend Usable
  usable Mixin, only: [:name, :from_spec]
end

Example.new.from_spec   # => "can be excluded"
Example.new.from_mixin  # => "always here"
Example.new.name        # => "defined by Mixin"
Example.ancestors       # => [Example, Mixin, Example::MixinUsableSpecUsed, Object, Kernel, BasicObject] (ruby -v 2.3.0)
```

Notice that Usable assigns the modified module to a constant with the same name as the given module, but with "Used" appended.
The main module and the spec were both included, but `Mixin` was not modified, so it didn't need a new name.

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'usable'
```

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake` 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/ridiculous/usable.