reduce object allocations

Example:

x = [1,2,3,4]
y = [3,2,1]

def test x, y
  hash = {}
  x.zip(y) { |k,v| hash[k] = v }
  hash
end

def test2 x, y
  Hash[x.zip(y)]
end

def test3 x, y
  x.zip(y).each_with_object({}) { |(k,v),hash| hash[k] = v }
end

def stat num
  start = GC.stat(:total_allocated_object)
  num.times { yield }
  total_obj_count = GC.stat(:total_allocated_object) - start
  puts "#{total_obj_count / num} allocations per call"
end

stat(100) { test(x,y) }
stat(100) { test2(x,y) }
stat(100) { test3(x,y) }

__END__
2 allocations per call
7 allocations per call
8 allocations per call

1 files changed, 4 insertions, 2 deletions

diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index 01378ae0ec..72c0aa61ee 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -184,7 +184,7 @@ module ActionDispatch
             private
 
             def optimized_helper(args)
-              params = Hash[parameterize_args(args)]
+              params = parameterize_args(args)
               missing_keys = missing_keys(params)
 
               unless missing_keys.empty?
@@ -203,7 +203,9 @@ module ActionDispatch
             end
 
             def parameterize_args(args)
-              @required_parts.zip(args.map(&:to_param))
+              params = {}
+              @required_parts.zip(args.map(&:to_param)) { |k,v| params[k] = v }
+              params
             end
 
             def missing_keys(args)