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  • delegate.rb

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SimpleDelegator

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__.

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

Public Instance Methods

__getobj__() click to toggle source

Returns the current object method calls are being delegated to.

 
               # File delegate.rb, line 264
def __getobj__
  @delegate_sd_obj
end
__setobj__(obj) click to toggle source

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

 
               # File delegate.rb, line 282
def __setobj__(obj)
  raise ArgumentError, "cannot delegate to self" if self.equal?(obj)
  @delegate_sd_obj = obj
end

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