M2compiler-V3/docs/summary_session-2026-09-29-oop.md

Session save — 2026-09-29: the OOP arc (Clarion CLASS, complete)

Suite 147/147; self-hosting fixpoint OK (bootstrap/fixpoint.sh, image 2,313,762 bytes). master, tree clean except the user's uncommitted compiler/toto.mod.

This session took Clarion CLASS from "declared + checked only, ends in 230" to a complete single-inheritance object system with dynamic dispatch — in four tagged steps, each re-verified against the byte-identical fixpoint.

Steps, tags and commits

Step	Tag	Commit	What
CHAR-array + + ConvResults	v3-charcat-convresults	5e2056f	(warm-up: string + test + ISO ConvResults)
Showcase 17	v3-showcase17	807ff9c	CLASS + strings + conversions together
CLASS lowering	v3-class-lowering	ed02804	fields, methods, THIS, single inheritance
VIRTUAL dispatch	v3-virtual-dispatch	98d3067	vtables + subtype pointers
Showcase 18	v3-showcase18	f584e62	polymorphic Shape hierarchy
CLASS finished	v3-class-finish	3804256	sibling calls + init body
Showcase 19	v3-showcase19	9f1f278	init body + sibling-call chain

1. CLASS lowering (v3-class-lowering)

• Layout — a class is a record: ComputeOffsets gives declaration-order offsets; single inheritance lays the child's fields after the parent's, and FindField/FieldOffset walk the parent chain. obj.field and WITH obj reuse the record path.
• Receiver — each method gets a hidden THIS VAR parameter, pushed as the current WITH base, so a bare field name means THIS^.field.
• Calls — obj.M(args) binds statically; the receiver is the hidden first argument; CLASS IMPLEMENTATION reuses the declared method symbol (matching call-site and definition uids).
• Docs: docs/summary_class-lowering.md.

2. VIRTUAL dispatch (v3-virtual-dispatch)

• 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.
• vptr — the introducing class gets an 8-byte vtable pointer (offset 0, or 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.
• dispatch — a virtual call loads the vptr, fetches the slot, and calls indirectly; subtyping lets POINTER TO Derived assign to POINTER TO Base.
• Docs: docs/summary_virtual-dispatch.md.

3. CLASS finished (v3-class-finish)

• Sibling-method calls — inside a CLASS IMPLEMENTATION, a bare method name is a call on THIS (chains work; a virtual sibling still dispatches through the vtable).
• Class BEGIN … END init body — emitted as <Class>_init and run once at startup.
• Multiple parents stay 230 (single inheritance by design).
• Docs: docs/summary_class-finish.md.

Showcases

• Showcase17 — a Bounded counter class + ConvResults + CHAR-array + → showcase17 total=42.
• Showcase18 — Circle/Square with a virtual Area(), driven through an array of POINTER TO Shape → showcase18 areas sum=139.
• Showcase19 — an init body setting a global plus a sibling-call chain → showcase19 total=42.

Tests (147)

Added across the arc: t_charcat, convresults_prog (+ conv_prog/ showcase14 moved to IntVal/RealVal), t_classmethod, t_classinherit, TClassDefProg (t_classdef.mod → t_classdef.def), t_virtual, t_classsibling, t_classinit (t_class promoted from reject), and Showcase17/18/19.

Where CLASS stands

✅ fields, methods (value/VAR formals, results), single inheritance, WITH, hidden THIS, VIRTUAL dynamic dispatch (vtables) with subtype pointers, sibling calls, init bodies. ⏸ multiple parents only (deliberate).

Resume

cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 147/147

Remaining polish (beyond OOP)

• VAL(LONGINT|REAL, x) and long→int narrowing.
• More stdlib (SysClock, richer Strings/Math).
• Files/IOChan extras (seek/pool nuances), deeper variant-record support.