DelegateWhenNil

This gem provides a macro-method, #delegate_when_nil, which works kind of like #delegate, except it evaluates the expression locally first, and delegates to the target only if the local result is nil.

class Parent
  attr_accessor :name, :address
  ...
end

class Child
  attr_accessor :name, :address
  delegate_when_nil :name, :address, to: :parent, prefix: :get

  # equivalent to
  # def get_name
  #   self.name || (parent && parent.get_name) # #get_name on Parent might delegate further...
  # end

# use #stop option to avoid the prefix on the parent attribute (delegation "stops" at parent)

class Child
  delegate_when_nil :name, :address, to: :parent, prefix: :get, stop: true

  # equivalent to
  # def get_name
  #   self.name || (parent && parent.name) # #name directly on parent instead of #get_name
  # end

Installation

Add this line to your application's Gemfile:

gem 'delegate_when_nil'

And then execute:

$ bundle

Or install it yourself as:

$ gem install delegate_when_nil

Usage

DelegateWhenNil installs itself in Module so is available everywhere in your code.

class Widget < PopularFramework::Base
  attr_accessor :parent
  attr_accessor :description, :colour, :height
  delegate_when_nil :description, :colour, :height, to: :parent, prefix: :get
  ...

In this example, if the #description, #colour, or #height properties are accessed and are nil, DelegateWhenNil will ask the #parent property instead.

p = Parent.new :description => "Woggle"
w = Widget.new :parent => p, :colour => :blue

w.get_description #=> "Woggle"
w.get_colour      #=> :blue

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request