Avoid unnecessary object allocation.

Author: lizhe

lib/grape/http/request.rb

@@ -1,10 +1,15 @@
 module Grape
   class Request < Rack::Request
+    ROUTING_ARGS = 'rack.routing_args'
+    HTTP_PREFIX  = 'HTTP_'
+    UNDERSCORE   = '_'
+    MINUS        = '-'
+
     def params
       @params ||= begin
         params = Hashie::Mash.new(super)
-        if env['rack.routing_args']
-          args = env['rack.routing_args'].dup
+        if env[ROUTING_ARGS]
+          args = env[ROUTING_ARGS].dup
           # preserve version from query string parameters
           args.delete(:version)
           args.delete(:route_info)
@@ -16,8 +21,11 @@ def params
 
     def headers
       @headers ||= env.dup.inject({}) do |h, (k, v)|
-        if k.to_s.start_with? 'HTTP_'
-          k = k[5..-1].tr('_', '-').downcase.gsub(/^.|[-_\s]./) { |x| x.upcase }
+        if k.to_s.start_with? HTTP_PREFIX
+          k = k[5..-1]
+          k.tr!(UNDERSCORE, MINUS)
+          k.downcase!
+          k.gsub!(/^.|[-_\s]./, &:upcase!)
           h[k] = v
         end
         h

lib/grape/util/stackable_values.rb

@@ -13,7 +13,10 @@ def initialize(inherited_values = {})
 
       def [](name)
         return @froozen_values[name] if @froozen_values.key? name
-        [@inherited_values[name], @new_values[name]].compact.flatten(1)
+        value = [@inherited_values[name], @new_values[name]]
+        value.compact!
+        value.flatten!(1)
+        value
       end
 
       def []=(name, value)