Class: SimpleDelegator

Inherits:
Delegator show all
Defined in:
lib/delegate.rb

Overview

A concrete implementation of Delegator, this class provides the means to delegate all supported method calls to the object passed into the constructor and even to change the object being delegated to at a later time with #__setobj__.

class User
  def born_on
    Date.new(1989, 9, 10)
  end
end

class UserDecorator < SimpleDelegator
  def birth_year
    born_on.year
  end
end

decorated_user = UserDecorator.new(User.new)
decorated_user.birth_year  #=> 1989
decorated_user.__getobj__  #=> #<User: ...>

A SimpleDelegator instance can take advantage of the fact that SimpleDelegator is a subclass of Delegator to call super to have methods called on the object being delegated to.

class SuperArray < SimpleDelegator
  def [](*args)
    super + 1
  end
end

SuperArray.new([1])[0]  #=> 2

Here’s a simple example that takes advantage of the fact that SimpleDelegator’s delegation object can be changed at any time.

class Stats
  def initialize
    @source = SimpleDelegator.new([])
  end

  def stats(records)
    @source.__setobj__(records)

    "Elements:  #{@source.size}\n" +
    " Non-Nil:  #{@source.compact.size}\n" +
    "  Unique:  #{@source.uniq.size}\n"
  end
end

s = Stats.new
puts s.stats(%w{James Edward Gray II})
puts
puts s.stats([1, 2, 3, nil, 4, 5, 1, 2])

Prints:

Elements:  4
 Non-Nil:  4
  Unique:  4

Elements:  8
 Non-Nil:  7
  Unique:  6

Instance Method Summary collapse

Methods inherited from Delegator

#!, #!=, #==, const_missing, delegating_block, #eql?, #freeze, #initialize, #marshal_dump, #marshal_load, #methods, #protected_methods, public_api, #public_methods, #respond_to_missing?

Constructor Details

This class inherits a constructor from Delegator

Instance Method Details

#__getobj__ ⇒ Object

Returns the current object method calls are being delegated to.



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# File 'lib/delegate.rb', line 305

def __getobj__
  unless defined?(@delegate_sd_obj)
    return yield if block_given?
    __raise__ ::ArgumentError, "not delegated"
  end
  @delegate_sd_obj
end

#__setobj__(obj) ⇒ Object

Changes the delegate object to obj.

It’s important to note that this does not cause SimpleDelegator’s methods to change. Because of this, you probably only want to change delegation to objects of the same type as the original delegate.

Here’s an example of changing the delegation object.

names = SimpleDelegator.new(%w{James Edward Gray II})
puts names[1]    # => Edward
names.__setobj__(%w{Gavin Sinclair})
puts names[1]    # => Sinclair



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# File 'lib/delegate.rb', line 327

def __setobj__(obj)
  __raise__ ::ArgumentError, "cannot delegate to self" if self.equal?(obj)
  @delegate_sd_obj = obj
end