virtual

Virtual method declaration.

Summary

A virtual method is a method which is inheritable and overridable. Since all methods in ruby are virtual, syntax is not required to provide this capability.

When developing framework style code, it is often required to override or implement a specific method in order to satisfy a contract. The purpose of this library is to provide a way for a developer of framework code to convey that intent.

The virtual library adds three macros to a class:

• virtual
• pure_virtual
• protocol

A virtual method is a method may be implemented in a subclass. A virtual method cannot be declared in a subclass that already has a concrete method of the same name.

A pure virtual method is a method must be implemented in a subclass. If it is not, an error will be raised when the method is called. A pure virtual method cannot be declared in a subclass that already has a concrete method of the same name. The pure_virtual macro is also aliased to abstract.

A protocol method is a specialization of a pure virtual method. It must be implemented in a subclass unless the subclass already has a concrete implementation of the same name.

Activation

The virtual and pure_virtual macros can be added to all classes with:

require 'virtual'
Virtual.activate

To avoid modifying the Object class, include the Virtual module directly in a class rather than activating it globally with Virtual.activate.

Example

class Something
  virtual :some_virtual_method
  pure_virtual :some_abstract_method
  pure_virtual :some_protocol_method
end

If the virtual library is not activated, the module can be included in the class:

class Something
  include Virtual

  virtual :some_virtual_method
  pure_virtual :some_abstract_method
  pure_virtual :some_protocol_method
end

The pure_virtual macro is also aliased to abstract:

class Something
  include Virtual

  abstract :some_abstract_method
end

License

The virtual library is released under the MIT License.