module HomogeneousDescendantLinkingNestable

Gives the ability to recursively access the next descendant object, or to find a given descendant at a specified index.

As the title of the module implies, descendants are singly linked by their immediate ancestor (i.e. parent), and a descendant is the same class as its parent. A parent has an instance variable to access then child object, but not the other way around; hence, singly nestable.

Classes that mix in this module need to be able to initialize properly without any parameters supplied to the initialize method.

Public Instance Methods

child!() click to toggle source

Gets the @child object if it is not nil. If it is nil, then a new instance of the same class as the calling object is created and assigned to @child, then child is returned.

# File lib/homogeneous_descendant_linking_nestable.rb, line 22
def child!
  @child = self.class.new if child_or_nil.nil?
  @child
end

child_or_nil() click to toggle source

Gets the next single descendant of the calling object. The child will be of the same class as the parent class.

# File lib/homogeneous_descendant_linking_nestable.rb, line 14
def child_or_nil
  @child
end

cutoff!() click to toggle source

Recursively nils out the descendant chain, starting with @child.

# File lib/homogeneous_descendant_linking_nestable.rb, line 28
def cutoff!
  @child.cutoff! unless @child.nil?
  @child = nil
end

descendant_at(index) click to toggle source

Gets the descendent object at the specified index.

@param index [Integer] the index of the descendant to retrieve @return the descendant at the specified index

# File lib/homogeneous_descendant_linking_nestable.rb, line 37
def descendant_at(index)
  i = 0
  c = self
  while i < index
    c = c.child_or_nil
    return nil if c.nil?

    i += 1
  end
  c
end