feat: add dsheet() interface

.storybook/drule.stories.js

@@ -22,5 +22,8 @@ storiesOf('drule()', module)
     h('div', {className: '' + className1}, 'Hello world')
   )
   .add('Dynamic styles', () =>
-    h('div', {className: className1({fontWeight: 'bold'})}, 'Hello world')
+    h('div', null,
+        h('div', {className: className1({fontWeight: 'bold'})}, 'Hello world'),
+        h('div', {className: className1({color: 'blue'})}, 'Hello world')
+    )
   )

addon/dsheet.js

@@ -0,0 +1,36 @@
+'use strict';
+
+exports.addon = function (renderer) {
+    if (process.env.NODE_ENV !== 'production') {
+        require('./__dev__/warnOnMissingDependencies')('dsheet', renderer, ['sheet', 'cache']);
+    }
+
+    renderer.dsheet = function (map, block) {
+        var styles = renderer.sheet(map, block);
+        var closures = {};
+
+        var createClosure = function (modifier) {
+            var closure = function (dynamicStyles) {
+                if (!dynamicStyles) {
+                    return styles[modifier];
+                }
+
+                var dynamicClassName = renderer.cache(dynamicStyles);
+
+                return styles[modifier] + dynamicClassName;
+            };
+
+            closure.toString = function () {
+                return styles[modifier];
+            };
+
+            return closure;
+        };
+
+        for (var modifier in map) {
+            closures[modifier] = createClosure(modifier);
+        }
+
+        return closures;
+    };
+};