Chapter 28.2

clox/src/memory.c

@@ -76,6 +76,11 @@ static void blackenObject(Obj *object) {
   printf("\n");
 #endif
   switch (object->type) {
+  case OBJ_BOUND_METHOD: {
+    ObjBoundMethod *bound = (ObjBoundMethod *)object;
+    markValue(bound->receiver);
+    markObject((Obj *)bound->method);
+  }
   case OBJ_CLASS: {
     ObjClass *klass = (ObjClass *)object;
     markObject((Obj *)klass->name);
@@ -117,6 +122,9 @@ static void freeObject(Obj *object) {
 #endif // DEBUG_LOG_GC
 
   switch (object->type) {
+  case OBJ_BOUND_METHOD:
+    FREE(ObjBoundMethod, object);
+    break;
   case OBJ_CLASS: {
     ObjClass *klass = (ObjClass *)object;
     freeTable(&klass->methods);

clox/src/object.c

@@ -25,6 +25,13 @@ static Obj *allocateObject(size_t size, ObjType type) {
   return object;
 }
 
+ObjBoundMethod *newBoundMethod(Value receiver, ObjClosure *method) {
+  ObjBoundMethod *bound = ALLOCATE_OBJ(ObjBoundMethod, OBJ_BOUND_METHOD);
+  bound->receiver = receiver;
+  bound->method = method;
+  return bound;
+}
+
 ObjClass *newClass(ObjString *name) {
   ObjClass *klass = ALLOCATE_OBJ(ObjClass, OBJ_CLASS);
   klass->name = name;
@@ -130,6 +137,9 @@ static void printFunction(ObjFunction *function) {
 
 void printObject(Value value) {
   switch (OBJ_TYPE(value)) {
+  case OBJ_BOUND_METHOD:
+    printFunction(AS_BOUND_METHOD(value)->method->function);
+    break;
   case OBJ_CLASS:
     printf("%s", AS_CLASS(value)->name->chars);
     break;

clox/src/object.h

@@ -8,6 +8,7 @@
 
 #define OBJ_TYPE(value) (AS_OBJ(value)->type)
 
+#define IS_BOUND_METHOD(value) isObjType(value, OBJ_BOUND_METHOD)
 #define IS_CLASS(value) isObjType(value, OBJ_CLASS)
 #define IS_CLOSURE(value) isObjType(value, OBJ_CLOSURE)
 #define IS_FUNCTION(value) isObjType(value, OBJ_FUNCTION)
@@ -15,6 +16,7 @@
 #define IS_NATIVE(value) isObjType(value, OBJ_NATIVE)
 #define IS_STRING(value) isObjType(value, OBJ_STRING)
 
+#define AS_BOUND_METHOD(value) ((ObjBoundMethod *)AS_OBJ(value))
 #define AS_CLASS(value) ((ObjClass *)AS_OBJ(value))
 #define AS_CLOSURE(value) ((ObjClosure *)AS_OBJ(value))
 #define AS_FUNCTION(value) ((ObjFunction *)AS_OBJ(value))
@@ -24,6 +26,7 @@
 #define AS_CSTRING(value) (((ObjString *)AS_OBJ(value))->chars)
 
 typedef enum {
+  OBJ_BOUND_METHOD,
   OBJ_CLASS,
   OBJ_CLOSURE,
   OBJ_FUNCTION,
@@ -87,6 +90,13 @@ typedef struct {
   Table fields;
 } ObjInstance;
 
+typedef struct {
+  Obj obj;
+  Value receiver;
+  ObjClosure *method;
+} ObjBoundMethod;
+
+ObjBoundMethod *newBoundMethod(Value receiver, ObjClosure *method);
 ObjClass *newClass(ObjString *name);
 ObjClosure *newClosure(ObjFunction *function);
 ObjFunction *newFunction();

clox/src/vm.c

@@ -108,6 +108,10 @@ static bool call(ObjClosure *closure, int argCount) {
 static bool callValue(Value callee, int argCount) {
   if (IS_OBJ(callee)) {
     switch (OBJ_TYPE(callee)) {
+    case OBJ_BOUND_METHOD: {
+      ObjBoundMethod *bound = AS_BOUND_METHOD(callee);
+      return call(bound->method, argCount);
+    }
     case OBJ_CLASS: {
       ObjClass *klass = AS_CLASS(callee);
       vm.stackTop[-argCount - 1] = OBJ_VAL(newInstance(klass));
@@ -130,6 +134,19 @@ static bool callValue(Value callee, int argCount) {
   return false;
 }
 
+static bool bindMethod(ObjClass *klass, ObjString *name) {
+  Value method;
+  if (!tableGet(&klass->methods, name, &method)) {
+    runtimeError("Undefined property '%s'.", name->chars);
+    return false;
+  }
+
+  ObjBoundMethod *bound = newBoundMethod(peek(0), AS_CLOSURE(method));
+  pop();
+  push(OBJ_VAL(bound));
+  return true;
+}
+
 static ObjUpvalue *captureUpvalue(Value *local) {
   ObjUpvalue *prevUpvalue = NULL;
   ObjUpvalue *upvalue = vm.openUpvalues;
@@ -305,9 +322,11 @@ static InterpretResult run() {
         break;
       }
 
-      runtimeError("Undefined property '%s'.", name->chars);
+      if (!bindMethod(instance->klass, name)) {
         return INTERPRET_RUNTIME_ERROR;
       }
+      break;
+    }
     case OP_SET_PROPERTY: {
       if (!IS_INSTANCE(peek(1))) {
         runtimeError("Only instances have fields.");