Hack to force bool only predicates

bool_only_predicates.rb

# Original: http://media.pragprog.com/titles/ruby4/code/metaprogramming/trace_calls.rb
#
# Modified to enforce opinionated predicate responses.
# Go buy and read the book!
# Note: This is **not** thread safe.
module BoolOnlyPredicates
  def self.included(klass)
    klass.instance_methods(false).each do |existing_method|
      wrap(klass, existing_method)
    end

    def klass.method_added(method)  # note: nested definition
      unless @force_calls_internal
        @force_calls_internal = true
        BoolOnlyPredicates.wrap(self, method)
        @force_calls_internal = false
      end
    end
  end

  def self.wrap(klass, method)
    return unless method.to_s.end_with?('?')
    klass.instance_exec do
      method_object = instance_method(method)

      define_method(method) do |*args, &block|
        !!method_object.bind(self).call(*args, &block)
      end
    end
  end
end

Object.include BoolOnlyPredicates

trace_calls.rb

# http://media.pragprog.com/titles/ruby4/code/metaprogramming/trace_calls.rb
#---
# Excerpted from "Programming Ruby 1.9 and 2.0",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material, 
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose. 
# Visit http://www.pragmaticprogrammer.com/titles/ruby4 for more book information.
#---
module TraceCalls
  def self.included(klass)
    klass.instance_methods(false).each do |existing_method|
      wrap(klass, existing_method)
    end
    def klass.method_added(method)  # note: nested definition
      unless @trace_calls_internal
        @trace_calls_internal = true
        TraceCalls.wrap(self, method)
        @trace_calls_internal = false
      end
    end
  end
  def self.wrap(klass, method)
    klass.instance_eval do
      method_object = instance_method(method)

      define_method(method) do |*args, &block|
        puts "==> calling #{method} with #{args.inspect}"
        result = method_object.bind(self).call(*args, &block)
        puts "<== #{method} returned #{result.inspect}"
        result
      end
    end
  end
end