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module ActiveSupport
# 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 <tt>ActiveRecord::Base</tt> at boot time purely to apply
# configuration. Instead a hook is registered that applies configuration once
# <tt>ActiveRecord::Base</tt> is loaded. Here <tt>ActiveRecord::Base</tt> 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)
module LazyLoadHooks
def self.extended(base) # :nodoc:
base.class_eval do
@load_hooks = Hash.new { |h,k| h[k] = [] }
@loaded = Hash.new { |h,k| h[k] = [] }
end
end
# Declares a block that will be executed when a Rails component is fully
# loaded.
def on_load(name, options = {}, &block)
@loaded[name].each do |base|
execute_hook(base, options, block)
end
@load_hooks[name] << [block, options]
end
def execute_hook(base, options, block)
if options[:yield]
block.call(base)
else
base.instance_eval(&block)
end
end
def run_load_hooks(name, base = Object)
@loaded[name] << base
@load_hooks[name].each do |hook, options|
execute_hook(base, options, hook)
end
end
end
extend LazyLoadHooks
end