Enum SubscriptBound 

pub enum SubscriptBound {
    Search(i64, bool),
    Math(String),
}

!!! WARNING: RUST-ONLY HELPER !!! Classification of ONE subscript operand — a range bound (${a[lo,hi]}) or a chained subscript (${a[lo,hi][SUB]}) — whose text may open with a (...) flag group.

C has no such function: getarg (c:Src/params.c:1367) parses the flags, runs the search and returns the index all in one pass, writing its side-effects back through Value *v / int *inv out-parameters. zshrs’s ported::params::getarg returns the matched ELEMENT for r/R and the INDEX for i/I (see getarg_out), and it has no Value to record v->isarr |= SCANPM_WANTVALS in — so the two facts every bound consumer needs (the match POSITION and whether WANTVALS was raised) are recovered here in one place instead of being re-derived at each call site.

Variants

Search(i64, bool)

c:Src/params.c:1729-1760 — the flag group ran a pattern SEARCH. .0 is getarg’s 1-based match index r (c:1758 returns 0 for a REVERSE miss, c:1751 len + 1 for a FORWARD miss); .1 records c:1523 v->isarr |= SCANPM_WANTVALS, raised by r/R/k/K when the i/I index flag (ind) is off.

Math(String)

c:Src/params.c:1597 r = mathevalarg(s, &s) — no search ran; the payload is the text to evaluate as arithmetic. A recognised but non-search flag group ((s.X.), (w), …) has been stripped; an UNKNOWN group is left in place because c:1477-1483’s flagerr arm rewinds to before the ( and re-reads the whole group as math.