Model filter unnecessarily re-constantizes strings

[tfausak]

The model filter spends a lot of time repeating work it's already done.

filter1 = ActiveInteraction::ModelFilter.new(:object)
filter2 = ActiveInteraction::ModelFilter.new(:object, class: Object)
filter3 = ActiveInteraction::ModelFilter.new(:object, class: :object)
filter4 = ActiveInteraction::ModelFilter.new(:object, class: 'Object')

n = 10_000
object = Object.new

Benchmark.bmbm do |bm|
  bm.report { n.times { filter1.cast(object) } } # => 0.235544
  bm.report { n.times { filter2.cast(object) } } # => 0.254362
  bm.report { n.times { filter3.cast(object) } } # => 0.253539
  bm.report { n.times { filter4.cast(object) } } # => 0.249165
end

Granted, that's not too slow. But it can be much, much faster. Caching the class speeds this up by two orders of magnitude.

module ActiveInteraction
  class ModelFilter < Filter
    def klass
      return @klass if instance_variable_defined?(:@klass)

      klass_name = options.fetch(:class, name).to_s.classify
      @klass ||= klass_name.constantize
    rescue NameError
      raise InvalidClassError, klass_name.inspect
    end
  end
end

  bm.report { n.times { filter1.cast(object) } } # => 0.002667
  bm.report { n.times { filter2.cast(object) } } # => 0.002707
  bm.report { n.times { filter3.cast(object) } } # => 0.005106
  bm.report { n.times { filter4.cast(object) } } # => 0.001633

I think we decided to naively re-constantize it every time to avoid something like cypriss/mutations#23.

[tfausak]

This is related to #91.