std/src/collections/vec/slice.nv - main - nv-lang/nova

std/src/collections/vec/slice.nv
54 строки3 KB
Evgeniy Golovin
merge: comment-hygiene-2 — чистка комментариев std (batch 1-20) + линт-свип 330→13
01 авг 2026, 18:13
01 авг 2026, 18:13bb8b33d
// std.collections.vec (slice) — zero-copy sub-range views, `Index[Range]`.
//
// `v[a..b]` returns a view of the SAME type `[]T` ≡ `Vec[T]` (a single
// `[]T` type — NOT a separate `Slice` type) sharing the parent buffer
// (interior pointer at `data + start`, `cap == len`). The GC keeps the parent
// buffer alive while the view is reachable (`GC_all_interior_pointers`). A
// subsequent reallocating mutation on the view (`push` at `cap == len`)
// detaches it into a fresh buffer, so it never mutates the parent (Go-model
// detach, GC-safe).
//
// `slice()` (a copying view whose name lied) was REMOVED; an owning copy is
// `clone()`. split_at/chunks/windows live on this same view model.
#prelude(core, runtime, collections, protocols)
module collections.vec

import std.collections.range.{Range}

// ──────────────────────────────────────────────────────────────────────────
// Range views (zero-copy slices) — `Index[Range]`
// ──────────────────────────────────────────────────────────────────────────

/// Zero-copy sub-range view — the slice `[r.start, r.end)` over the same
/// backing buffer. Powers `v[a..b]` (Plan 194 Ф.3 vrange-routing, closes
/// [M-172.14-vrange-nv-route]): `emit_c.rs` synthesizes `v.index(range)` for
/// `v[a..b]` and dispatches here through the normal method-call path — there
/// is no more codegen range-slice intrinsic (`nova_vec_slice_chk`/`_nochk`
/// are retired). Overloads with `@index(i int)` (access.nv).
///
/// Slice-bounds are a `requires` precondition. Justification: a `requires` is
/// never unsafely elided — enforced at runtime under `checked`, and under
/// `optimized` sound-elided ONLY when Z3 proves the range in-bounds (else
/// enforced). So bounds get the ideal profile (zero-cost when provably safe,
/// checked otherwise) through the SINGLE contract machinery — one window, not
/// a hand-written guard plus a separate site-elision path. On violation → a
/// contract panic. The perf goal (0-alloc view-descriptor placement) is met
/// via the general sret `_out` call-site rewrite
/// (`sret_maybe_rewrite_call`) — any Leaf-form Vec-returning mono method gets
/// it automatically, so this body needs no special plumbing.
export fn Vec[T] @index(r Range) -> Self
    requires r.start >= 0 && r.end >= r.start && r.end <= @len
{
    ro n = r.end - r.start
    Self { data: unsafe { @data.offset(r.start) }, len: n, cap: n }
}

/// Safe zero-copy sub-range view — `Some(view)` when `[r.start, r.end)` is in
/// bounds, `None` otherwise. The non-panicking counterpart of `@index(Range)`.
export fn Vec[T] @get(r Range) -> Option[Self] {
    if r.start < 0 || r.end < r.start || r.end > @len {
        return None
    }
    ro n = r.end - r.start
    Some(Self { data: unsafe { @data.offset(r.start) }, len: n, cap: n })
}