# 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

```sh
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.