---
title: MyGem.configure Block
teaser: How to write conventional configuration code in Ruby.
tags: web,ruby,clearance
author: Dan Croak
published_on: 2010-01-20
---

We recently enhanced [Clearance](http://github.com/thoughtbot/clearance) with a
configuration block that could be used in `config/initializers/clearance.rb`.

I liked the way [Airbrake](http://airbrake.io) did it and wanted to implement
the same pattern:

```ruby
Airbrake.configure do |config|
  config.api_key = 'your_key_here'
end
```

Here's the implementation:

```ruby
module Clearance
  class << self
    attr_accessor :configuration
  end

  def self.configure
    self.configuration ||= Configuration.new
    yield(configuration)
  end

  class Configuration
    attr_accessor :mailer_sender

    def initialize
      @mailer_sender = 'donotreply@example.com'
    end
  end
end
```

The `configure` class method stores a `Configuration` object inside the
`Clearance` module.

Anything set from the `configure` block is an `attr_accessor` on the
`Configuration` class.

So now `config/initializers/clearance.rb` is possible:

```ruby
Clearance.configure do |config|
  config.mailer_sender = 'donotreply@example.com'
end
```

Easy for the application developer to understand. Clean internal implementation:

```ruby
Clearance.configuration.mailer_sender
```

In the library's tests, set configuration attributes without worrying about
undefining constants:

```ruby
Clearance.configuration.mailer_sender= 'new.email@example.com'
```

Yay.