gistfile1.rbx

class Foo
  def self.capping_bar
    alias_method :orig_bar, :bar
    def bar; 'BAR'; end
    yield
    alias_method :bar, :orig_bar
	end
	
	def bar; 'bar'; end
end

f = Foo.new

Foo.capping_bar do
  puts f.bar
end

puts f.bar