Posted By

pmccann on 05/12/07

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Last Edited at 05/12/07 04:39pm

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Verifier objects

/ Published in: Ruby

Niiice... (stolen from linked site via planetrubyonrails.com)

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# Encapsulates some object and executes expressions
# in the context of that object tracking the result 
# of the evaluation. As soon as an expression is 
# false, the verification fails.
#
#   verification = Verifier.new('Marcel') do
#     try { size == 6 } # Passes
#     try { size == 5 } # Fails
#     try { raise }     # Doesn't get here
#   end
#
#   verification.verify
#   => false
class Verifier
  class FailedVerification < Exception
  end
  
  class << self
    def verify(object, &block)
      new(object, &block).verify
    end
  end
  
  attr_reader :object, :results, :block
  def initialize(object, &block)
    @object   = object
    @results  = []
    @verified = false
    @block    = block
  end
  
  def verified?
    @verified && results.all?
  end
  
  def verify
    instance_eval(&block)
    @verified = true
  rescue FailedVerification
    false
  end
  
  def try(&block)
    results << object.instance_exec(&block)
    raise FailedVerification if results.last == false
  end
end

URL: http://project.ioni.st/post/1211#snippet_1211

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