[add] Added VarStore.

sjplayer/src/sjplayer/Context.d

@@ -17,19 +17,19 @@ import sjplayer.Actor,
        sjplayer.ElementInterface,
        sjplayer.ProgramSet,
        sjplayer.ScheduledControllerInterface,
-       sjplayer.VarStoreInterface;
+       sjplayer.VarStore;
 
 ///
 class Context {
  public:
   ///
   this(ParametersBlock[] params, ProgramSet programs) {
-    auto builder  = new Builder;
-    auto varstore = new BlackHole!VarStoreInterface;
-
     actor_      = new Actor(programs.Get!ActorProgram);
     background_ = new Background(programs.Get!BackgroundProgram);
 
+    auto builder  = new Builder;
+    auto varstore = new VarStore(actor_);
+
     import sjplayer.BackgroundScheduledController,
            sjplayer.CircleElementScheduledController;
     auto factories = tuple(

sjplayer/src/sjplayer/VarStore.d

@@ -0,0 +1,29 @@
+/// License: MIT
+module sjplayer.VarStore;
+
+import std.exception,
+       std.format;
+
+import sjplayer.Actor,
+       sjplayer.VarStoreInterface;
+
+///
+class VarStore : VarStoreInterface {
+ public:
+  ///
+  this(in Actor actor) {
+    actor_ = actor;
+  }
+
+  override float opIndex(string name) const {
+    switch (name) {
+      case "actor_x": return actor_.pos.x;
+      case "actor_y": return actor_.pos.y;
+
+      default: throw new Exception("unknown variable %s".format(name));
+    }
+  }
+
+ private:
+  const Actor actor_;
+}