Chapter 28.4

clox/src/compiler.c

@@ -51,7 +51,12 @@ typedef struct {
   bool isLocal;
 } Upvalue;
 
-typedef enum { TYPE_FUNCTION, TYPE_METHOD, TYPE_SCRIPT } FunctionType;
+typedef enum {
+  TYPE_FUNCTION,
+  TYPE_INITIALIZER,
+  TYPE_METHOD,
+  TYPE_SCRIPT
+} FunctionType;
 
 typedef struct Compiler {
   struct Compiler *enclosing;
@@ -159,7 +164,12 @@ static int emitJump(uint8_t instruction) {
 }
 
 static void emitReturn() {
-  emitByte(OP_NIL);
+  if (current->type == TYPE_INITIALIZER) {
+    emitBytes(OP_GET_LOCAL, 0);
+  } else {
+    emitByte(OP_NIL);
+  }
+
   emitByte(OP_RETURN);
 }
 
@@ -389,6 +399,11 @@ static void method() {
   uint8_t constant = identifierConstant(&parser.previous);
 
   FunctionType type = TYPE_METHOD;
+  if (parser.previous.length == 4 &&
+      memcmp(parser.previous.start, "init", 4) == 0) {
+    type = TYPE_INITIALIZER;
+  }
+
   function(type);
   emitBytes(OP_METHOD, constant);
 }
@@ -588,6 +603,10 @@ static void returnStatement() {
   if (match(TOKEN_SEMICOLON)) {
     emitReturn();
   } else {
+    if (current->type == TYPE_INITIALIZER) {
+      error("Can't return a value from an initializer.");
+    }
+
     expression();
     consume(TOKEN_SEMICOLON, "Expect ';' after return value.");
     emitByte(OP_RETURN);

clox/src/memory.c

@@ -180,6 +180,7 @@ static void markRoots() {
 
   markTable(&vm.globals);
   markCompilerRoots();
+  markObject((Obj *)vm.initString);
 }
 
 static void traceReferences() {

clox/src/vm.c

@@ -65,12 +65,16 @@ void initVM() {
   initTable(&vm.globals);
   initTable(&vm.strings);
 
+  vm.initString = NULL;
+  vm.initString = copyString("init", 4);
+
   defineNative("clock", clockNative);
 }
 
 void freeVM() {
   freeTable(&vm.globals);
   freeTable(&vm.strings);
+  vm.initString = NULL;
   freeObjects();
 }
 
@@ -116,6 +120,13 @@ static bool callValue(Value callee, int argCount) {
     case OBJ_CLASS: {
       ObjClass *klass = AS_CLASS(callee);
       vm.stackTop[-argCount - 1] = OBJ_VAL(newInstance(klass));
+      Value initializer;
+      if (tableGet(&klass->methods, vm.initString, &initializer)) {
+        return call(AS_CLOSURE(initializer), argCount);
+      } else if (argCount != 0) {
+        runtimeError("Expected 0 arguments but got %d.", argCount);
+        return false;
+      }
       return true;
     }
     case OBJ_CLOSURE:

clox/src/vm.h

@@ -23,6 +23,7 @@ typedef struct {
   Value *stackTop;
   Table globals;
   Table strings;
+  ObjString *initString;
   ObjUpvalue *openUpvalues;
 
   size_t bytesAllocated;