Andrew Kesterson
05f241aca1
A scalar now lives in the variable record (`akbasic_Variable::inlinevalue`) rather than drawing from the value pool, so a `GOSUB` local, a `FOR` counter and a `DEF` parameter cost nothing at all. The pool is a bump allocator with no free, and its comment justified that with "nothing in BASIC destroys a variable". Scope exit does: it marks the variable slot unused, `new_variable()` memsets the slot it hands back -- clearing `values` -- and `variable_init()` therefore took *fresh* slots for a variable whose old ones were still counted. Every scope that created a local leaked, with no diagnostic until the pool ran dry on whichever line happened to be unlucky. Six thousand `GOSUB`s creating one local used to die on the 4091st at `LOC# = 1` with "Array of 1 elements does not fit in the 0 remaining value slots". They now run. A `DEF` called eight thousand times used to die between the four and five thousandth -- the leaking slot was the call scope's parameter, which is a scalar -- and both forms now run. A game creating one name per tick was dead in half a minute; the Breakout in examples/ was, after twenty-five seconds. **A `@` name is the one exclusion, and it is the whole of it.** A structure or a pointer to one keeps pool storage, because a pointer into a record outlives the scope that DIMmed it -- docs/16-structures.md says nothing is reclaimed and `prev_environment()` relies on it. The name suffix is the right test rather than `structtype`, which the DIM path sets *after* calling `variable_init()`. A local array therefore still leaks, deliberately, and is now the narrow rule the tutorial teaches. `SWAP` needed the other half: it copies whole variable records, so the `values` pointer that came over named the other variable's inline slot -- which by then held this variable's own old value -- and SWAP silently did nothing. Caught by tests/language/housekeeping/verbs.bas, which is the golden corpus earning its keep. tests/value_pool.c is the new coverage. It asserts the mechanism as well as the consequence: a later change that moved arrays inline too would pass every behavioural case and quietly break the pointer guarantee. The sharpest case takes the pool's whole 4096 slots in four arrays after two hundred scope entries, so one leaked slot has nowhere to go. Chapter 17 Step 3 taught "declare every name at the top" and no longer needs to. It now teaches what is still true -- a name first seen inside a subroutine dies at RETURN, so a routine cannot answer its caller through one -- and its demonstration is the array case, which still fails. TODO.md section 6 item 30 and section 9 item 1, both struck. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
7.5 KiB
7.5 KiB