Performance and memory usage fixes (rails-api#2309)

* Use select and reject instead of partition.map

* Sort adapters keys in place

* Just select from options

* Add changelog entry

Author: krzysiek1507

CHANGELOG.md

@@ -11,6 +11,7 @@ Fixes:
 - [#2307](https://github.com/rails-api/active_model_serializers/pull/2307) Falsey attribute values should not be reevaluated.
 
 Misc:
+- [#2309](https://github.com/rails-api/active_model_serializers/pull/2309) Performance and memory usage fixes
 
 ### [v0.10.8 (2018-11-01)](https://github.com/rails-api/active_model_serializers/compare/v0.10.7...v0.10.8)
 

lib/active_model/serializer/lazy_association.rb

@@ -9,7 +9,7 @@ class Serializer
       delegate :collection?, to: :reflection
 
       def reflection_options
-        @reflection_options ||= reflection.options.dup.reject { |k, _| !REFLECTION_OPTIONS.include?(k) }
+        @reflection_options ||= reflection.options.select { |k, _| REFLECTION_OPTIONS.include?(k) }
       end
 
       def object

lib/active_model_serializers/adapter.rb

@@ -37,7 +37,7 @@ def adapter_map
 
       # @return [Array<Symbol>] list of adapter names
       def adapters
-        adapter_map.keys.sort
+        adapter_map.keys.sort!
       end
 
       # Adds an adapter 'klass' with 'name' to the 'adapter_map'

lib/active_model_serializers/serializable_resource.rb

@@ -16,8 +16,8 @@ class SerializableResource
     # @return the serializable_resource, ready for #as_json/#to_json/#serializable_hash.
     def initialize(resource, options = {})
       @resource = resource
-      @adapter_opts, @serializer_opts =
-        options.partition { |k, _| ADAPTER_OPTION_KEYS.include? k }.map { |h| Hash[h] }
+      @adapter_opts = options.select { |k, _| ADAPTER_OPTION_KEYS.include? k }
+      @serializer_opts = options.reject { |k, _| ADAPTER_OPTION_KEYS.include? k }
     end
 
     def serialization_scope=(scope)