feat: implement invoking initializers

next chapter: Initializer return values

Author: aymaneelmaini

src/memory.c

@@ -218,6 +218,7 @@ static void mark_roots()
 
     mark_table(&vm.globals);
     mark_compiler_roots();
+    mark_object((Obj*)vm.init_string);
 }
 
 static void trace_references()

src/vm.c

@@ -63,6 +63,9 @@ void init_VM()
     init_table(&vm.globals);
     init_table(&vm.strings);
 
+    vm.init_string = NULL;
+    vm.init_string = copy_string("init", 4);
+
     vm.bytes_allocated = 0;
     vm.next_GC = 1024 * 1024;
 
@@ -77,6 +80,7 @@ void free_VM()
 {
     free_table(&vm.globals);
     free_table(&vm.strings);
+    vm.init_string = NULL;
     free_objects();
 }
 
@@ -131,6 +135,18 @@ static bool call_value(Value callee, int arg_count)
         case OBJ_INSTANCE:
             ObjClass* klass = AS_CLASS(callee);
             vm.stack_top[-arg_count - 1] = OBJ_VAL(new_instance(klass));
+
+            Value initializer;
+            if (table_get(&klass->methods, vm.init_string, &initializer))
+            {
+                return call(AS_CLOSURE(initializer), arg_count);
+            }
+            else if (arg_count != 0)
+            {
+                runtime_error("Expected 0 arguments but got %d", arg_count);
+                return false;
+            }
+
             return true;
         case OBJ_CLOSURE:
             return call(AS_CLOSURE(callee), arg_count);

src/vm.h

@@ -25,6 +25,7 @@ typedef struct
     Value*      stack_top;
     Table       globals;
     Table       strings;  // for string interning just like (string pool in java)
+    ObjString*  init_string;
     ObjUpvalue* open_upvalues;
     size_t      bytes_allocated;
     size_t      next_GC;