h2. Active Support Overview

Active Support is the Rails component responsible for providing Ruby language extensions, utilities, and other transversal stuff. It offers a richer bottom-line at the language level, targeted both at the development of Rails applications, and at the development of Rails itself.

By referring to this guide you will learn:

* The extensions to the Ruby core modules and classes provided by Rails.
* The rest of fundamental libraries available in Rails.

endprologue.

h3. Extensions to +Kernel+

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h3. Extensions to +Object+

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h3. Extensions to +Module+

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h3. Extensions to +Class+

h4. Class Attribute Accessors

The macros +cattr_reader+, +cattr_writer+, and +cattr_accessor+ are analogous to their +attr_*+ counterparts but for classes. They initialize a class variable to +nil+ unless it already exists, and generate the corresponding class methods to access it:

<ruby>
class MysqlAdapter < AbstractAdapter
  # Generates class methods to access @@emulate_booleans.
  cattr_accessor :emulate_booleans
  self.emulate_booleans = true
end
</ruby>

Instance methods are created as well for convenience. For example given

<ruby>
module ActionController
  class Base
    cattr_accessor :logger
  end
end
</ruby>

we can access +logger+ in actions. The generation of the writer instance method can be prevented setting +:instance_writer+ to +false+ (not any false value, but exactly +false+):

<ruby>
module ActiveRecord
  class Base
    # No pluralize_table_names= instance writer is generated.
    cattr_accessor :pluralize_table_names, :instance_writer => false
  end
end
</ruby>

h4. Class Inheritable Attributes

Class variables are shared down the inheritance tree. Class instance variables are not shared, but they are not inherited either. The macros +class_inheritable_reader+, +class_inheritable_writer+, and +class_inheritable_accessor+ provide accesors for class-level data which is inherited but not shared with children:

<ruby>
module ActionController
  class Base
    # The value of allow_forgery_protection is inherited,
    # but its value in a particular class does not affect
    # the value in the rest of the controllers hierarchy.
    class_inheritable_accessor :allow_forgery_protection
  end
end
</ruby>

They accomplish this with class instance variables and cloning on subclassing, there are no class variables involved. Cloning is performed with +dup+ as long as the value is duplicable.

There are some variants specialised in arrays and hashes:

<ruby>
class_inheritable_array_writer
class_inheritable_array

class_inheritable_hash_writer
class_inheritable_hash
</ruby>

Those writers take any inherited array or hash into account and extend them rather than overwrite them.

As with vanilla class attribute accessors these macros create convenience instance methods for reading and writing. The generation of the writer instance method can be prevented setting +:instance_writer+ to +false+ (not any false value, but exactly +false+):

<ruby>
module ActiveRecord
  class Base
    class_inheritable_accessor :default_scoping, :instance_writer => false
  end
end
</ruby>

h3. Extensions to +NilClass+

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h3. Extensions to +TrueClass+

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h3. Extensions to +FalseClass+

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h3. Extensions to +Symbol+

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h3. Extensions to +String+

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h3. Extensions to +Numeric+

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h3. Extensions to +Integer+

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h3. Extensions to +Float+

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h3. Extensions to +BigDecimal+

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h3. Extensions to +Enumerable+

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h3. Extensions to +Array+

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h3. Extensions to +Hash+

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h3. Extensions to +Range+

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h3. Extensions to +Proc+

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h3. Extensions to +Date+

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h3. Extensions to +DateTime+

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h3. Extensions to +Time+

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h3. Extensions to +Process+

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h3. Extensions to +Pathname+

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h3. Extensions to +File+

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h3. Extensions to +Exception+

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h3. Extensions to +NameError+

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h3. Extensions to +LoadError+

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h3. Extensions to +CGI+

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h3. Extensions to +Benchmark+

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h3. Changelog

"Lighthouse ticket":https://rails.lighthouseapp.com/projects/16213/tickets/67

* April 18, 2009: Initial version by "Xavier Noria":credits.html#fxn
