RCR 224: temporary enabled global variable

turn a global variable on before invokation of a method call, and restore its value when the method returns.

while debugging testcases, then you sometimes want verbose output, and other times you want no output. However its not easy to enable/disable output!

Above situation could be solved by letting a global variable control when the debug_puts outputs to stdout.

The syntax could be like

temporary_enable(variable_name, methods)

Below is a simplified copy of a testcase of mine. The debug controls a global variable, which controls when to output debug information. I can easily control what is going on by inserting or removing comments.

class TestScanner < Common::TestCase

  module Works
    include ExercisesSequence
    include ExercisesAlternation
    include ExercisesRepeat
  end 
  module Todo
    include ExercisesRepeatNested 
    debug :test_repeat_nested4
    undef test_repeat_nested4   # activate_next set wrong node as DONE
    debug :test_repeat_nested2
    #debug :test_repeat_nested3
    #undef test_repeat_nested2   # activate_next fix cause trouble
    #undef test_repeat_nested3   # activate_next fix cause trouble
  end
  include Works
  include Todo

end

The temporary_enable method should probably be added to the class Module, in order to make it usable within modules.

class Module

  def temporary_enable(variable, *method_names)
    temp_methods = private_instance_methods(true)
    method_names.each do |symbol| 
      name = symbol.id2name
      org = "_debug_"+name
      if temp_methods.include?(org)
        $stderr.puts "ERROR: already enabled method: #{name}"
        next
      end
      begin
        meth = instance_method(symbol)
      rescue => e
        $stderr.puts "ERROR: symbol2method failure, " + e.inspect
        next
      end  
      arguments = (meth.arity != 0) ? "(*a,&b)" : "(&b)"
      alias_method org, name
      module_eval %{
        def #{name}#{arguments}
          old, $#{variable} = $#{variable}, true
          return #{org}#{arguments}
        ensure
          $#{variable} = old
        end
        private :#{org}
      }
    end
  end

end

if $0 == __FILE__

  $global = false
  class A
    def test
      puts "A#test  global=#{$global}"
    end
    #temporary_enable("global", :test)
  end
  A.new.test

end