Dependencies

依赖。

Class Cache

[] & get

clear!

empty?

key?

safe_get

store

Watch Stack

each

new_constants

watch_namespaces

watching?

另：

自动加载会从 app/models, app/controllers, lib/ and other load paths.等加载，如果没有会：

# in active_support/dependencies.rb
def const_missing(const_name)
  from_mod = anonymous? ? guess_for_anonymous(const_name) : self
  Dependencies.load_missing_constant(from_mod, const_name)
end

然后：

#lib/active_support/dependencies.rb:477
expanded = File.expand_path(file_path)
expanded.sub!(/\.rb\z/, '')

if loading.include?(expanded)
  raise "Circular dependency detected while autoloading constant #{qualified_name}"
end

此处有魔法。