Add self_referring_obj macro for self-referential objects.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/obj/fun.rs

@@ -31,24 +31,18 @@ pub struct UserFun {
 
 impl UserFun {
     pub fn new_obj(code: Vec<Inst>, locals: FunLocals) -> UserFunRef {
-        let obj_ref = ObjRef::new(UserFun {
+        self_referring_obj! (
+            Self {
                 vtable: Default::default(), // this is a placeholder for the real vtable
                 attrs: Default::default(),
                 code: Arc::new(code),
                 locals,
-        });
+            },
-
+            vtable: |obj_ref: ObjRef| vtable! {
-        // XXX replace the vtable before returning, since __call__ member points to the object
-        // itself
-        {
-            write_obj!(let obj = obj_ref);
-            obj.vtable = vtable! {
                 TY_MEMBER_NAME.sym => USER_FUN_TY.clone(),
                 CALL_MEMBER_NAME.sym => obj_ref.clone(),
-            };
             }
-
+        )
-        obj_ref
     }
 
     pub fn code(&self) -> &Vec<Inst> {
@@ -209,24 +203,17 @@ pub struct NativeFun {
 
 impl NativeFun {
     pub fn new_obj(fun: NativeFunPtr) -> ObjRef<Self> {
-        let obj_ref = ObjRef::new(Self {
+        self_referring_obj! (
+            Self {
                 vtable: Default::default(),
                 attrs: Default::default(),
                 fun: GcSafeWrapper::new(fun),
-        });
+            },
-
+            vtable: |obj_ref: ObjRef| vtable! {
-
-        // XXX replace the vtable before returning, since __call__ member points to the object
-        // itself
-        {
-            write_obj!(let obj = obj_ref);
-            obj.vtable = vtable! {
                 TY_MEMBER_NAME.sym => NATIVE_FUN_TY.clone(),
                 CALL_MEMBER_NAME.sym => obj_ref.clone(),
-            };
             }
-
+        )
-        obj_ref
     }
 
     /// Gets the native function that can be invoked.

src/obj/macros.rs

@@ -122,3 +122,19 @@ macro_rules! handle_type {
         impl shredder::EmptyScan for $name {}
     };
 }
+
+#[macro_export]
+macro_rules! self_referring_obj {
+    ($init:expr $(, $name:ident : $value:expr)* $(,)?) => {{
+        let obj_ref = $crate::obj::ObjRef::new($init);
+
+        {
+            write_obj!(let obj = obj_ref);
+            $(
+                obj.$name = ($value)(obj_ref.clone());
+            )*
+        }
+
+        obj_ref
+    }};
+}