Cache calculated params

Author: ajjahn

lib/react/component/props_wrapper.rb

@@ -27,15 +27,17 @@ def self.define_param(name, param_type)
           end
         else
           define_method("#{name}") do
-            if param_type.respond_to? :_react_param_conversion
-              param_type._react_param_conversion props[name]
-            elsif param_type.is_a?(Array) &&
-              param_type[0].respond_to?(:_react_param_conversion)
-              props[name].collect do |param|
-                param_type[0]._react_param_conversion param
+            fetch_from_cache(name) do
+              if param_type.respond_to? :_react_param_conversion
+                param_type._react_param_conversion props[name]
+              elsif param_type.is_a?(Array) &&
+                param_type[0].respond_to?(:_react_param_conversion)
+                props[name].collect do |param|
+                  param_type[0]._react_param_conversion param
+                end
+              else
+                props[name]
               end
-            else
-              props[name]
             end
           end
         end
@@ -51,6 +53,18 @@ def [](prop)
 
       private
 
+      def fetch_from_cache(name)
+        last, value = cache[name]
+        return value if last.equal?(props[name])
+        yield.tap do |value|
+          cache[name] = [props[name], value]
+        end
+      end
+
+      def cache
+        @cache ||= Hash.new { |h, k| h[k] = [] }
+      end
+
       def props
         component.props
       end

spec/react/param_declaration_spec.rb

@@ -169,7 +169,6 @@ def render
 
     describe "converts params only once" do
       it "not on every access" do
-        pending 'Fix after merging'
         stub_const "BazWoggle", Class.new
         BazWoggle.class_eval do
           def initialize(kind)
@@ -187,7 +186,6 @@ def render
             "#{params.foo.kind}"
           end
         end
-        expect(Foo).to render
         expect(React.render_to_static_markup(React.create_element(Foo, foo: {bazwoggle: 1}))).to eq('<span>2</span>')
       end