The #94 Option-C vstream surface was left incomplete and structurally
divergent from Hare: constructors heap-allocated and returned (X | nomem)
or used out-params instead of Hare's by-value stack ownership; memio lacked
reset/buffer/borrowedread; bufio's scanner was never ported to the vtable.
This is the additive half of the eFinal collapse — OLD surface stays fully
live; the destructive FLIP (delete OLD + drop _v + repoint) is the next
commit.
Reshape all constructors to VALUE-RETURN (field-by-field sret; the heap +
nomem was an unnecessary crutch — wide slice-bearing struct return-by-value
is byte-id-proven, cf 925_sret_struct_return_run). memio fixed/dynamic/
dynamicfrom, bufio init, log new now return the struct by value; the nomem
is gone with the alloc that forced it.
memio: unify the per-flavour ctx structs onto one `stream` (vt at offset 0);
collapse fixed_string + dynamic_string into a single string() over the common
header (bare-str return is the ratified rule-9 frombytes carve-out, cited at
the site per ref/hare/memio/stream.ha:81); port reset/buffer/borrowedread as
single fns over the header.
bufio: collapse the EXISTING scanner subset (newscannerbuf/scanbyte/scanbytes/
scanline/finish + setflush/flush/unread/isbuffered) onto the vtable, with src
now io.vstream so reads go through io.st_read. The Hare scanner functions ww
never implemented (scanrune/scanstring-arbitrary-delim/readtok/readline/
auto-grow newscanner) are out of scope and deferred to #217 — eFinal is a
collapse, not a feature expansion.
Keep the explicit (&fn): *io.T casts on vtable-slot stores (cgen-neutral;
avoids the #214 (X|void) over-acceptance surface; dropping the casts is a
deferred #206 payoff gated on #214).
Self-gate: 776 (memio) 18/18 and 778 (bufio) 27/27, every row carrying a
cs.s == ww.s byte-id check — bufio/fmt/log are not compiler-embedded, so
these rows are their only byte-id coverage. 779/781 stay STAGE_CS-only
pending #209. Regen w6c+wwdump combined.ww (io+memio are the embedded
modules).
Hojun-Cho
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