module_creation_helper ¶ ↑

module_creation_helper adds a helper method for creating new modules and classes at runtime.

API

• rdoc.info/github/pluginaweek/module_creation_helper/master/frames

Bugs

• github.com/pluginaweek/module_creation_helper/issues

Development

• github.com/pluginaweek/module_creation_helper

Testing

• travis-ci.org/pluginaweek/module_creation_helper

Source

• git://github.com/pluginaweek/module_creation_helper.git

Mailing List

• groups.google.com/group/pluginaweek-talk

Creating modules and classes at runtime isn’t the easiest and most intuitive process. Although often used for anonymous classes, there are many times where you will want to associate a runtime class with an actual name.

Traditionally, you would create new classes like so:

c = Class.new               # => #<Class:0x480e388>
Object.const_set('Foo', c)  # => Foo

Although this isn’t very hard, there are two problems: (1) It’s a repetitive process that should be DRYed. (2) Callbacks that are invoked while the class is being created do not know the name of the class.

To understand the second problem, consider the following:

class Foo
  def self.inherited(base)
    puts "inherited class: #{base}, name: #{base.name}"
  end
end

When a class inherits from Foo, Ruby will invoke the inherited callback. For example,

c = Class.new(Foo)
# inherited class: #<Class:0x47fb92c>, name:
# => #<Class:0x47fb92c>

As you can see from output in this example, since the class has not yet been assigned to a constant, it is anonymous and does not yet have a name.

To address these issues, the functionality is encapsulated into a new method, Module#create. Since the method is defined in Module, it is also available to Class since Class inherits from Module.

Using the same example as before,

c = Class.create('Bar', :superclass => Foo)
# inherited class: Bar, name: Bar
# => Bar

As you can see, the name of the class is now available during the inherited callback and is automatically assigned to the ‘Bar’ constant in Object.

In addition to specifying the superclass, you can also specify the parent module/class like so:

c = Class.create('Bar', :superclass => Foo, :parent => MyModule)
# inherited class: MyModule::Bar, name: MyModule::Bar
# => MyModule::Bar

As you normally could when creating a new class, you can provide an additional block that defines the body of the class. For example,

c = Class.create('Bar', :superclass => Foo, :parent => MyModule) do
  def say_hello
    'hello'
  end
end
# inherited class: MyModule::Bar, name: MyModule::Bar
# => Bar
Bar.new.say_hello
# => "hello"

None.