[objects] Implement a more space-efficient V3SplitObjectModel

src/engine/Type.v3

@@ -398,28 +398,56 @@ class HeapTypeDecl(final: bool, supertypes: Array<HeapType>) extends Decl {
 enum Packedness { UNPACKED, PACKED_I8, PACKED_I16 }
 type StorageType(valtype: ValueType, pack: Packedness, mutable: bool) { }
 
+// Information added to a struct declaration, specific to the object model.
+class StructDeclInfo {
+	var next: StructDeclInfo;
+}
+
 // Struct type declaration. (ext:gc)
 class StructDecl extends HeapTypeDecl {
 	def field_types: Array<StorageType>;
 	def defaultable = allHaveDefaultValues(field_types);
+	var infos: StructDeclInfo; // extended information about a struct
 
 	new(final: bool, supertypes: Array<HeapType>, field_types) super(final, supertypes) {}
 
 	def render(buf: StringBuilder) -> StringBuilder {
 		return putUid(buf.put1("struct #%d", heaptype_index));
 	}
+	def addInfo(info: StructDeclInfo) -> this {
+		info.next = infos;
+		this.infos = info;
+	}
+	def getInfo<T>() -> T {
+		for (s = infos; s != null; s = s.next) if (T.?(s)) return T.!(s);
+		return T.default;
+	}
+}
+
+// Information added to an array declaration, specific to the object model.
+class ArrayDeclInfo {
+	var next: ArrayDeclInfo;
 }
 
 // Array type declaration. (ext:gc)
 class ArrayDecl extends HeapTypeDecl {
 	def elem_types: Array<StorageType>;
 	def defaultable = allHaveDefaultValues(elem_types);
+	var infos: ArrayDeclInfo; // extended information about an array
 
 	new(final: bool, supertypes: Array<HeapType>, elem_types) super(final, supertypes) {}
 
 	def render(buf: StringBuilder) -> StringBuilder {
 		return putUid(buf.put1("array #%d", heaptype_index));
 	}
+	def addInfo(info: ArrayDeclInfo) -> this {
+		info.next = infos;
+		this.infos = info;
+	}
+	def getInfo<T>() -> T {
+		for (s = infos; s != null; s = s.next) if (T.?(s)) return T.!(s);
+		return T.default;
+	}
 }
 
 // Continuation type declaration. (ext:stack-switching)