prototype of efficient inline template expansion

gistfile1.rbx

# Prototype of a mechanism for efficient inline template compilation
# via call site caching.
require 'merb-core'
require 'merb-haml'

END {
  require 'rbench'

  expando = Expando.new
  
  # make sure that the different methods are generating the same output for the sake of fairness
  raise "haml's not fair" unless expando.efficient_haml == expando.naive_haml
  raise "erb's not fair" unless expando.efficient_erb == expando.naive_erb


  # Compare this approach to inline use of haml or erubis
  # Results on my machine:
  #                      |   naive | efficient | naive/expand |
  # -----------------------------------------------------------
  # haml          x10000 |   2.642 |     0.652 |        4.05x |
  # erb           x10000 |   1.393 |     0.443 |        3.15x |
  RBench.run(10_000) do
    column :times
    column :naive,  :title => "naive"
    column :expand,  :title => "efficient"
    column :diff, :title => "naive/expand", :compare => [:naive,:expand]

    report "haml" do
      expand do
        expando.efficient_haml
      end
      naive do
        expando.naive_haml
      end
    end
  
    report "erb" do
      expand do
        expando.efficient_erb
      end
      naive do
        expando.naive_erb
      end
    end
  end
}

###################################################################

module Templatizer
  FakeIo = Struct.new :read, :path

  def expand_static_template(type, string, values={})
    context = caller[0]
    mname = :"__expanded__#{context.gsub(%r{\W}, '_')}"

    extend ::Merb::InlineTemplates
    unless respond_to? mname
      string = _dedent string
      io = FakeIo.new string, context.scan(/.*?:\d+/).first
      Merb::Template.engine_for(".#{type}").compile_template(io, mname, values.keys, ::Merb::InlineTemplates)
    end

    send(mname, values)
  end
  
  def _dedent string
    min_size = Float::MAX
    string.scan(/^( *)\S/).each do |indentation, ignored|
      min_size = [min_size, indentation.length].min
    end
    string.gsub(/^ {0,#{min_size}}/, '')
  end
end

class Object
  include Templatizer
end

###################################################################

class Expando
  def initialize
    @instance = "YO"
  end

  def efficient_haml
    expand_static_template(:haml, <<-HAML, :a => 1)
      = @instance
      = a
    HAML
  end

  def naive_haml
    # Not fair to dedent here.
    haml = Haml::Engine.new <<-EOS
= @instance
= a
    EOS
  
    haml.render self, :a => 1
  end
  
  def efficient_erb
    expand_static_template(:erb, <<-ERB, :a => 1)
      <%= @instance %>
      <%= a         %>
    ERB
    
  end
  
  def naive_erb
    # Not fair to dedent here.

    eruby = ::Erubis::BlockAwareEruby.new(<<-ERB)
<%= @instance %>
<%= @a         %>
    ERB
    
    eruby.evaluate :a => 1, :instance => @instance
  end
end