lazy_load_hooks allows rails to lazily load a lot of components and thus making the app boot faster. Because of this feature now there is no need to require ActiveRecord::Base at boot time purely to apply configuration. Instead a hook is registered that applies configuration once ActiveRecord::Base is loaded. Here ActiveRecord::Base is used as example but this feature can be applied elsewhere too.

Here is an example where on_load method is called to register a hook.

initializer "active_record.initialize_timezone" do
  ActiveSupport.on_load(:active_record) do
    self.time_zone_aware_attributes = true
    self.default_timezone = :utc
  end
end

When the entirety of activerecord/lib/active_record/base.rb has been evaluated then run_load_hooks is invoked. The very last line of activerecord/lib/active_record/base.rb is:

ActiveSupport.run_load_hooks(:active_record, ActiveRecord::Base)

The TimeZone class serves as a wrapper around TZInfo::Timezone instances. It allows us to do the following:

• Limit the set of zones provided by TZInfo to a meaningful subset of 142 zones.

• Retrieve and display zones with a friendlier name (e.g., “Eastern Time (US & Canada)” instead of “America/New_York”).

• Lazily load TZInfo::Timezone instances only when they’re needed.

• Create ActiveSupport::TimeWithZone instances via TimeZone’s local, parse, at and now methods.

If you set config.time_zone in the Rails Application, you can access this TimeZone object via Time.zone:

# application.rb:
class Application < Rails::Application
  config.time_zone = "Eastern Time (US & Canada)"
end

Time.zone       # => #<TimeZone:0x514834...>
Time.zone.name  # => "Eastern Time (US & Canada)"
Time.zone.now   # => Sun, 18 May 2008 14:30:44 EDT -04:00

The version of TZInfo bundled with Active Support only includes the definitions necessary to support the zones defined by the TimeZone class. If you need to use zones that aren’t defined by TimeZone, you’ll need to install the TZInfo gem (if a recent version of the gem is installed locally, this will be used instead of the bundled version.)

XmlMini LibXML implementation using a SAX-based parser

XmlMini JRuby JDOM implementation

XmlMini Nokogiri implementation using a SAX-based parser

XmlMini ReXML implementation

XmlMini Nokogiri implementation

XmlMini LibXML implementation

This class has dubious semantics and we only have it so that people can write params[:key] instead of params['key'] and they get the same value for both keys.

Some code from jeremymcanally’s “pending” github.com/jeremymcanally/pending/tree/master