Session summary — 2026-09-29 (b): VIRTUAL dispatch + showcase18

Suite 144/144; self-hosting fixpoint OK (image 2,310,300 bytes). master, tree clean except the user's uncommitted compiler/toto.mod.

This session completed the Clarion OOP story by adding dynamic dispatch, then showcased it.

Steps, tags and headline commits

Step	Tag	Commit	What
VIRTUAL dispatch	`v3-virtual-dispatch`	`98d3067`	per-class vtables + subtype pointer assignment
Showcase	`v3-showcase18`	(this commit)	polymorphic Shape hierarchy

1. VIRTUAL dispatch (vtables)

VIRTUAL methods now resolve at run time. A base-class pointer holding a derived object calls the derived override:

TYPE
  CLASS Shape;  VIRTUAL PROCEDURE Area() : INTEGER; END Shape;
  CLASS Circle (Shape); VIRTUAL PROCEDURE Area() : INTEGER; END Circle;
...
VAR b : POINTER TO Shape; c : POINTER TO Circle;
BEGIN
  NEW(c); b := c;            (* subtype pointer assignment *)
  ExitCode := b^.Area()      (* Circle.Area, decided at run time *)
END

vtable — each class with virtuals owns a slice of a shared pool: the parent's slots are inherited first; a same-named virtual method overrides in place; new ones append. Each method node records its vslot.
vptr — the class introducing virtuals gets an 8-byte vtable pointer (offset 0 with no parent, else after the parent's fields); subclasses share it, so an object's vptr identifies its dynamic class.
emission — data $vt_<typeindex> = { l $Method_uid, … }; a declared-but-unimplemented method is l 0.
init — static class variables and NEW store the vptr.
dispatch — a virtual call loads the vptr, fetches the slot, and calls indirectly; the receiver is the hidden first argument.
subtyping — POINTER TO Derived assigns to POINTER TO Base (IsSubclass), which lets a base pointer hold a derived object.

Docs: docs/summary_virtual-dispatch.md.

2. Showcase

compiler/tests/showcase18.mod (Showcase18, exit 42): a Shape hierarchy (Circle, Square) with a virtual Area(); an array of POINTER TO Shape holds objects of both kinds and each area is resolved at run time; the sum is asserted and printed:

showcase18 areas sum=139

(The number is built with Conversions.IntToStr + CHAR-array +, tying in the earlier stdlib/string work.)

Tests (144, was 143)

New: t_virtual (3) and Showcase18 (42).

Resume

cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 144/144

Remaining polish

CLASS: bare sibling-method calls inside a method body, a class BEGIN … END init body, multiple parents.
VAL(LONGINT|REAL, x) and long→int narrowing.
More stdlib (SysClock, richer Strings/Math).

summary_showcase18.md 2.8 KB Постійне посилання Історія Запис