Issue 260 - [Typed objects] Implement type inheritance

lib/typedObjects/objectTypes.js

Index: lib/typedObjects/objectTypes.js
===================================================================
--- a/lib/typedObjects/objectTypes.js
+++ b/lib/typedObjects/objectTypes.js
@@ -106,94 +106,175 @@ function createSetter(typeId, offset)
 {
   typeId = typeId | 0;
   offset = offset | 0;
 
   let views = Array.prototype.slice.call(arguments, 2);
   let reference = new Reference(types, views);
   return function(value)
   {
-    if (value && value.typeId != typeId)
+    if (value && !isInstance(typeId, value))
       throw new Error("Incompatible type");
 
     reference.bufferIndex = this.bufferIndex | 0;
     reference.byteOffset = (this.byteOffset | 0) + offset;
     if (value)
     {
       reference.typeId = value.typeId;
       reference.targetBufferIndex = value.bufferIndex;
       reference.targetByteOffset = value.byteOffset;
     }
     else
       reference.typeId = -1;
   };
 }
 
-function ObjectType(properties, meta)
+/**
+ * Overridden methods get the respective method of the superclass as the first
+ * parameter. This function will create a wrapper function for the method that
+ * forwards all arguments to the actual methods but also injects super as first
+ * parameter.
+ */
+function createSubclassMethod(method, super_)
+{
+  return function()
+  {
+    let args = [].slice.apply(arguments);
+    args.unshift(() => super_.apply(this, arguments));
+    return method.apply(this, args);
+  };
+}
+
+function extend(parentTypeInfo, typeDescriptor, meta)
 {
   if (typeof meta != "object" || meta == null)
     meta = {};
 
-  let propList = [];
-  let proto = {};
+  let properties = Object.create(parentTypeInfo && parentTypeInfo.properties);
+
+  // Methods have to be actually copied here, prototypes won't work correctly
+  // with Object.defineProperties().
+  let methods = Object.create(null);
+  if (parentTypeInfo)
+    for (let key in parentTypeInfo.methods)
+      methods[key] = parentTypeInfo.methods[key];
+
   let maxReferenceLength = TypedReference.byteLength | 0;
-  for (let name in properties)
+  for (let name in typeDescriptor)
   {
-    let type = properties[name];
+    let type = typeDescriptor[name];
     if (type && typeof type.referenceLength == "number")
     {
+      if (name in methods)
+        throw new Error("Property " + name + " masks a method with the same name");
+      if (name in properties)
+      {
+        if (properties[name] == type)
+          continue;
+        else
+          throw new Error("Cannot redefine type of property " + name + " in subclass");
+      }
+
       // Property with type
-      propList.push([name, type]);
+      properties[name] = type;
 
       let referenceLength = type.referenceLength | 0;
       if (referenceLength > maxReferenceLength)
         maxReferenceLength = referenceLength;
     }
     else if (typeof type == "function")
     {
       // Method
-      Object.defineProperty(proto, name, fixedPropertyDescriptor(type));
+      if (name in properties)
+        throw new Error("Method " + name + " masks a property with the same name");
+
+      if (name in methods)
+        type = createSubclassMethod(type, methods[name].value);
+      methods[name] = fixedPropertyDescriptor(type);
     }
     else
       throw new Error("Unrecognized type " + type + " given for property " + name);
   }
 
+  let proto = {};
   let buffers = [];
   let viewTypes = [];
   let views = [];
-  let byteLength = defineProperties(proto, propList, viewTypes, views, 0);
+  let byteLength = defineProperties(proto, properties, viewTypes, views, 0);
+  Object.defineProperties(proto, methods);
 
   // Round up to be a multiple of the maximal property size
   byteLength = ((byteLength - 1) | (maxReferenceLength - 1)) + 1;
 
   // We need to be able to store a typed reference in the object's buffer
   byteLength = Math.max(byteLength, TypedReference.byteLength) | 0;
   let typedReferenceViews = getViewsForType(TypedReference, viewTypes, views);
 
+  // Take constructor from meta parameter, allow calling superclass constructor.
+  let constructor = parentTypeInfo && parentTypeInfo.constructor;
+  if (meta.hasOwnProperty("constructor") && typeof meta.constructor == "function")
+  {
+    if (constructor)
+      constructor = createSubclassMethod(meta.constructor, constructor);
+    else
+      constructor = meta.constructor;
+  }
+
   let typeId = types.length | 0;
   let typeInfo = {
     byteLength: byteLength,
     bufferSize: "bufferSize" in meta ? Math.max(meta.bufferSize | 0, 2) : 128,
     firstFree: new TypedReference(typeId, typedReferenceViews),
     proto: proto,
+    properties: properties,
+    methods: methods,
     buffers: buffers,
     viewTypes: viewTypes,
     views: views,
     typeId: typeId,
-    constructor: (meta.hasOwnProperty("constructor") && typeof meta.constructor == "function" ? meta.constructor : null)
+    parentTypeInfo: parentTypeInfo,
+    constructor: constructor
   };
 
   let result = create.bind(typeInfo);
   Object.defineProperties(result, {
     byteLength: fixedPropertyDescriptor(byteLength),
 
     referenceLength: fixedPropertyDescriptor(Reference.byteLength),
     viewTypes: fixedPropertyDescriptor(Reference.viewTypes),
 
     typeId: fixedPropertyDescriptor(typeId),
+    extend: fixedPropertyDescriptor(extend.bind(null, typeInfo)),
+    isInstance: fixedPropertyDescriptor(isInstance.bind(null, typeId)),
 
     createGetter: fixedPropertyDescriptor(createGetter),
     createSetter: fixedPropertyDescriptor(createSetter.bind(null, typeId))
   });
   types.push(typeInfo);
   return result;
 }
-exports.ObjectType = ObjectType;
+
+function isInstance(typeId, obj)
+{
+  typeId = typeId | 0;
+
+  // TODO: This could be optimized by compiling the list of all subclasses for
+  // each type up front. Question is whether this is worth it.
+  let typeInfo = types[obj.typeId | 0];
+  while (typeInfo)
+  {
+    if ((typeInfo.typeId | 0) == typeId)
+      return true;
+    typeInfo = typeInfo.parentTypeInfo;
+  }
+  return false;
+}
+
+let ObjectBase = exports.ObjectBase = extend(null, {
+  equals: function(obj)
+  {
+    if (!obj)
+      return false;
+    return this.typeId == obj.typeId && this.bufferIndex == obj.bufferIndex && this.byteOffset == obj.byteOffset;
+  }
+}, null);
+
+exports.ObjectType = ObjectBase.extend;