Configurations

Configurations provides a unified approach to do configurations using the MyGem.configure do ... end idiom with the flexibility to do everything from arbitrary configurations to type asserted configurations for your gem or any other ruby code.

Install

gem install configurations

or with Bundler

gem 'configurations', '~> 2.2.0'

Configurations uses Semver 2.0

Compatibility

Compatible with MRI 1.9.2 - 2.2, Rubinius 2.x, jRuby 1.7 and 9K

Why?

There are various ways to do configurations, yet there seems to be a broad consensus on the MyGem.configure do ... end idiom. So instead of rolling your own, you can add this gem to your gem and get that functionality for free, plus some goodies you may want but do not have the time to write like type assertion or nested configurations.

Less time copy pasting configuration code, more time writing exciting code for you.

Configure

First way: Arbitrary Configuration

Go boom! with ease. This allows your gem / code users to set any value they like.

module MyGem
  include Configurations
end

Gives your users:

MyGem.configure do |c|
  c.foo.bar.baz = 'fizz'
  c.hi = 'Hello-o'
  c.class = 'oooh wow' # Such flexible!
end

Gives you:

MyGem.configuration.class #=> 'oooh wow'
MyGem.configuration.foo.bar.baz #=> 'fizz'

Undefined properties on an arbitrary configuration will return nil

MyGem.configuration.not_set #=> nil

If you want to define the behaviour for not set properties yourself, use not_configured. You can either define a catch-all not_configured which will be executed whenever you call a value that has not been configured and has no default:

module MyGem
  not_configured do |prop|
    raise NoMethodError, "#{prop} must be configured"
  end
end

Or you can define finer-grained callbacks:

module MyGem
  not_configured my: { nested: :prop } do |prop|
    raise NoMethodError, "#{prop} must be configured"
  end
end

Second way: Restricted Configuration

If you just want some properties to be configurable, consider this option

module MyGem
  include Configurations
  configurable :foo, bar: :baz, biz: %i(bi ba bu)
end

Gives your users:

MyGem.configure do |c|
  c.foo = 'FOO'
  c.bar.baz = 'FIZZ'
  c.biz.bi = 'BI'
  c.biz.ba = 'BA'

  # This would raise NoMethodError
  # c.bar.biz
end

Gives you:

MyGem.configuration.foo #=> 'FOO'
MyGem.configuration.bar.baz #=> 'FIZZ'

Not configured properties on a restricted configuration will raise NoMethodError

MyGem.configuration.not_set #=> <#NoMethodError>

If you want to define the behaviour for not set properties yourself, use not_configured. This will only affect properties set to configurable. All not configurable properties will raise NoMethodError.

module MyGem
  not_configured :awesome, :nice do |prop| # omit the arguments to get a catch-all not_configured
    warn :not_configured, "Please configure #{prop} or live in danger: youtube.com/watch?v=yZ15vCGuvH0"
  end
end

Third way: Type Restricted Configuration

If you want to make sure your configurations only accept one type, consider this option

module MyGem
  include Configurations
  configurable String, :foo
  configurable Array, bar: :baz
end

Gives your users:

MyGem.configure do |c|
  c.foo = 'FOO'
  c.bar.baz = %w(hello)

  # This would raise Configurations::ConfigurationError
  # c.foo = :not_so_foo
  # c.bar.baz = 'oh my cannot configure'
end

Fourth way: Custom asserted or changed values

If you need further assertions or you need to change a value before it gets stored in the configuration, consider passing a block

module MyGem
  include Configurations
  configurable :foo do |value|

    # The return value is what gets assigned, unless it is nil,
    # in which case the original value persists
    #
    value + ' ooooh my'
  end
  configurable String, bar: :baz do |value|

    # value is guaranteed to be a string at this point
    #
    unless %w(bi ba bu).include?(value)
      raise ArgumentError, 'baz needs to be one of bi, ba, bu'
    end
  end
end

Gives your users:

MyGem.configure do |c|
  c.foo = 'FOO'
  c.bar.baz = %w(bi)

  # This would raise the ArgumentError in the block
  # c.bar.baz = %w(boooh)
end

Gives you:

MyGem.configuration.foo #=> 'FOO ooooh my'
MyGem.configuration.bar.baz #=> one of %w(bi ba bu)

Configuration Methods

You might want to define methods on your configuration which use configuration values to bring out another value. This is what configuration_method is here to help you with:

module MyGem
  include Configurations
  configurable :foo, :bar
  configuration_method :foobar do |arg|
    foo + bar + arg
  end
end

Your users do:

MyGem.configure do |c|
  c.foo = 'FOO'
  c.bar = 'BAR'
end

You get:

MyGem.configuration.foobar('ARG') #=> 'FOOBARARG'

configuration methods can also be installed on nested properties using hashes:

configuration_method foo: :bar do |arg|
  foo + bar + arg
end

Defaults:

module MyGem
  include Configurations
  configuration_defaults do |c|
    c.foo.bar.baz = 'BAR'
  end
end

Get a hash if you need it

MyGem.configuration.to_h #=> a Hash

Configure with a hash where needed

Sometimes your users will have a hash of configuration values which are not handy to press into the block form. In that case, they can use from_h inside the configure block to either read in the full or a nested configuration. With a everything besides arbitrary configurations, from_h can also be used outside the block.

yaml_hash = YAML.load_file('configuration.yml')

MyGem.configure do |c|
  c.foo = 'bar'
  c.baz.from_h(yaml_hash)
end

Some caveats

Reserved Methods

These are reserved methods on the configuration instance and should not be defined:

• initialize
• inspect
• method_missing
• object_id
• singleton_class
• to_h
• to_s

Configuration inherits from BasicObject, so method names defined through Kernel and Object are available.

Thread safety

Configuration is synchronized. Re-configuration via the configure block switches out the configuration in place rather than mutating its properties, so don't hold on to configuration objects in another context. That said, please bear in mind that keeping mutable state in configurations is as bad an idea as every other kind of global mutable state, if you expect values to change at runtime, configurations are not the right place to keep them:

Encourage your users to configure once when initializing the environment, reconfigure on reload, but never ever at runtime.

Contributing

YES!

Let's make this awesome. Write tests for your added stuff, bonus points for feature branches. If you don't have the time to write a fix, raise an issue.

Copyright

Copyright © 2015 Beat Richartz. See LICENSE.txt for further details.