class MyClass
  def foo; 42; end
end
class MyOtherClass
  def bar; 43; end
end
a = MyClass.new
b = MyOtherClass.new
a.foo
b.bar

class MyClass
  def foo
    $stderr.puts "#{self}#foo => 42"
    42
  end
end
class MyOtherClass
  def bar
    $stderr.puts "#{self}#bar => 43"
    43
  end
end
a = MyClass.new
b = MyOtherClass.new
a.foo
b.bar

class MyClass
  def foo
    raise "SecurityError" unless $roles.include?("MyClass#foo")
    $stderr.puts "#{self}#foo => 42"
    42
  end
end
class MyOtherClass
  def bar
    raise "SecurityError" unless $roles.include?("MyClass#bar")
    $stderr.puts "#{self}#bar => 43"
    43
  end
end
a = MyClass.new
b = MyOtherClass.new
$roles = [ "MyClass#foo" ]
a.foo
b.bar

class MyClass
  def foo
    # YUCK!: raise "SecurityError" unless $roles.include?("MyClass#foo")
    # YUCK!: $stderr.puts "#{self}#foo => 42"
    42
  end
end
class MyOtherClass
  def bar
    # YUCK!: raise "SecurityError" unless $roles.include?("MyClass#bar")
    # YUCK!: $stderr.puts "#{self}#bar => 43"
    43
  end
end
a = MyClass.new
b = MyOtherClass.new
$roles = [ "MyClass#foo" ] # ???
a.foo
b.bar

# Advice 
trace_advice = CheapAdvice.new(:around) do | ar, body |
  ar.advice[:log] << 
    "#{Time.now.iso8601(6)} " <<
    "#{ar.rcvr.class} #{ar.meth} #{ar.rcvr.object_id}\n"
  body.call
  ar.advice[:log] << 
    "#{Time.now.iso8601(6)} " <<
    "#{ar.rcvr.class} #{ar.meth} #{ar.rcvr.object_id} " <<
    "=> #{ar.result.inspect}\n"    
end
# State attached to trace_advice.
trace_advice[:log] = File.open("trace.log", "a+")

...
# Activate trace_advice:
trace_advice.advise!(MyClass, :foo)
trace_advice.advise!(MyOtherClass, :bar)
a.foo
b.bar

# Disable trace_advice:
trace_advice.disable!
a.foo
b.bar

:advice:
  ~:
    :enabled: false
    :options:
      :trace:
        :logger:
          :name: :default

  'MyClass':
    :advice:  trace

  'MyClass#foo':
    :enabled: false

  'MyClass#bar':
    :enabled: false