Method: Module#class_inheritor

Defined in:
lib/core/facets/module/class_inheritor.rb

#class_inheritor(key, obj, op = nil, &fop) ⇒ Object

Class Inheritor

Create an dynamic class inheritable attribute.

Inheritor providse a means to store and inherit data via the class heirarchy. An inheritor creates two methods one named after the key that provides a reader. And one named after key! which provides the writer. (Because of the unique nature of inheritor the reader and writer can’t be the same method.)

The first argument is the inheritor’s name. The second argument is the archtype object. This object must be duplicable (via #dup). The last argument is either the symbolic operator/method or a block that specifies how one hierarchical level “integrates” with the next.

class X
  class_inheritor :x, [], :+
end

class Y < X
end

X.x! << :a
X.x  #=> [:a]
Y.x  #=> [:a]

Y.x! << :b
X.x  #=> [:a]
Y.x  #=> [:a, :b]

NOTE: Adding an inheritor directly to Module or Class will probably not do what is expected. Thankfully that usecase is likely a YAGNI, but in anycase it is even more likely that it is not possible with this code.

NOTE: This method is not a common core extension and is not loaded automatically when using require 'facets'.

CREDIT: Thomas Sawyer

Raises:

  • (ArgumentError)

Uncommon:

  • require ‘facets/module/class_inheritor’



48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
 
# File 'lib/core/facets/module/class_inheritor.rb', line 48

def class_inheritor(key, obj, op=nil, &fop)
  raise ArgumentError if op && fop

  if !fop
    op  = op ? op.to_sym : :+
    fop = lambda{ |o, x| o.__send__(op, x) }
  end

  #(class << self; self; end).module_eval do
  class_extend do

    define_method(key) do
      ancestors.reverse.inject(obj.dup) do |o, a|
        if a.respond_to?("#{key}!")
          fop.call(o, a.__send__("#{key}!"))
        else
          o
        end
      end
    end

    define_method("#{key}!") do
      if instance_variable_defined?("@#{key}")
        instance_variable_get("@#{key}")
      else
        instance_variable_set("@#{key}", obj.dup)
      end
    end

  end
end