Remove each_with_object where it's slow.

Remember #1128?
Unfortunately, calling `each_with_object` on `Hash` is not a good idea
(`inject` has the same problem btw).

It allocates an array for each `(k,v)` pair which is not good.

More details here: rails/rails@960de47
@tenderlove excellently covered it all.

Author: marshall-lee

lib/grape/formatter/serializable_hash.rb

@@ -21,9 +21,11 @@ def serialize(object)
           elsif object.is_a?(Array) && !object.map { |o| o.respond_to? :serializable_hash }.include?(false)
             object.map(&:serializable_hash)
           elsif object.is_a?(Hash)
-            object.each_with_object({}) do |(k, v), h|
+            h = {}
+            object.each_pair do |k, v|
               h[k] = serialize(v)
             end
+            h
           else
             object
           end

lib/grape/middleware/base.rb

@@ -55,9 +55,11 @@ def content_type
       end
 
       def mime_types
-        content_types.each_with_object({}) do |(k, v), types_without_params|
+        types_without_params = {}
+        content_types.each_pair do |k, v|
           types_without_params[v.split(';').first] = k
         end
+        types_without_params
       end
     end
   end

lib/grape/request.rb

@@ -2,27 +2,39 @@ module Grape
   class Request < Rack::Request
     HTTP_PREFIX = 'HTTP_'.freeze
 
+    alias_method :rack_params, :params
+
     def params
-      @params ||= begin
-        params = Hashie::Mash.new(super)
-        if env[Grape::Env::RACK_ROUTING_ARGS]
-          args = env[Grape::Env::RACK_ROUTING_ARGS].dup
-          # preserve version from query string parameters
-          args.delete(:version)
-          args.delete(:route_info)
-          params.deep_merge!(args)
-        end
-        params
-      end
+      @params ||= build_params
     end
 
     def headers
-      @headers ||= env.each_with_object({}) do |(k, v), h|
+      @headers ||= build_headers
+    end
+
+    private
+
+    def build_params
+      params = Hashie::Mash.new(rack_params)
+      if env[Grape::Env::RACK_ROUTING_ARGS]
+        args = env[Grape::Env::RACK_ROUTING_ARGS].dup
+        # preserve version from query string parameters
+        args.delete(:version)
+        args.delete(:route_info)
+        params.deep_merge!(args)
+      end
+      params
+    end
+
+    def build_headers
+      headers = {}
+      env.each_pair do |k, v|
         next unless k.to_s.start_with? HTTP_PREFIX
 
         k = k[5..-1].split('_').each(&:capitalize!).join('-')
-        h[k] = v
+        headers[k] = v
       end
+      headers
     end
   end
 end

lib/grape/util/strict_hash_configuration.rb

@@ -64,7 +64,8 @@ def self.nested_settings_methods(setting_name, new_config_class)
           end
 
           define_method 'to_hash' do
-            merge_hash = setting_name.keys.each_with_object({}) { |k, hash| hash[k] = send("#{k}_context").to_hash }
+            merge_hash = {}
+            setting_name.each_key { |k| merge_hash[k] = send("#{k}_context").to_hash }
 
             @settings.to_hash.merge(
               merge_hash