Module: Anise::Annotation

Defined in:

lib/anise/annotation.rb

Overview

The Annotate module is the core of the Anise system. It provides the framework for annotating class or module related objects, typically symbols representing methods, with arbitrary metadata. These annotations do not do anything in themselves. They are simply data. But they can be put to good use. For instance an attribute validator might check for an annotation called :valid and test against it.

Synopsis

require 'anise/annotation'

class X
  include Anise::Annotation

  attr :a

  ann :a, :desc => "A Number"
end

X.ann(:a, :desc)  #=> "A Number"

As stated, annotations need not only annotate methods, they are arbitrary, so they can be used for any purpose. For example, we may want to annotate instance variables.

class X
  include Anise::Annotation

  ann :@a, :valid => lambda{ |x| x.is_a?(Integer) }

  def validate
    instance_variables.each do |iv|
      if validator = self.class.ann(iv)[:valid]
        value = instance_variable_get(iv)
        unless validator.call(value)
          raise "Invalid value #{value} for #{iv}"
        end
      end
    end
  end
end

Or, we could even annotate the class itself.

class X
  include Anise::Annotate

  ann self, :valid => lambda{ |x| x.is_a?(Enumerable) }
end

Although annotations are arbitrary they are tied to the class or module they are defined against.

– TODO: By using a global variable rather the definining a class

instance variable for each class/module, it is possible to
quicky scan all annotations for the entire system. To do
the same without this would require scanning through
the ObjectSpace. Should we do this?
  $annotations = Hash.new { |h,k| h[k] = {} }

TODO: The ann(x).name notation is kind of nice. Would like to add that

back-in if reasonable. This would require @annotations to be an
OpenHash or OpenObject rather than just a Hash though.

++

Defined Under Namespace

Modules: Aid

Class Method Summary

• .included(base) ⇒ Object

Class Method Details

.included(base) ⇒ Object

# File 'lib/anise/annotation.rb', line 72

def self.included(base)
  base.extend Aid
end