Module altrep 

Core ALTREP types and registration traits.

Architecture

• FFI: Raw setters/types in crate::sys::altrep
• Traits: Safe traits in crate::altrep_traits (Altrep, AltVec, AltInteger, etc.)
  • Required methods: Compiler-enforced by trait definition
  • Optional methods: Gated by HAS_* constants, defaults provided
• Bridge: Generic extern "C-unwind" trampolines in crate::altrep_bridge
• High-level data traits: crate::altrep_data (AltrepLen + Alt*Data) — implement with &self methods instead of raw SEXP.
• SEXP wrapper: crate::altrep_sexp — !Send + !Sync wrapper that prevents an ALTREP SEXP from crossing thread boundaries before materialization.
• Derive: #[derive(AltrepInteger)] / AltrepReal / AltrepLogical / AltrepRaw / AltrepString / AltrepComplex / AltrepList on a struct emits everything below: Altrep, AltVec, the family-specific trait, AltrepLen, Alt*Data, an impl RegisterAltrep, and the R_make_alt* registration. See the altrep_derive module in the miniextendr-macros crate for the attribute reference and validation rules.

Two code paths

1. Field-based derive (default) — annotate fields with #[altrep(len = "field", elt = "field", class = "Name")] and the derive handles length/elt/registration.
2. Manual — #[altrep(manual)] skips AltrepLen / Alt*Data so you hand-roll those traits (custom elt, no_na, sum, …); the impl_alt*_from_data! registration is still emitted.

Both paths route trampolines through the same guard mode selected by Altrep::GUARD; guard modes are documented on crate::altrep_traits.

Threading

ALTREP callbacks run on R’s main thread — they receive raw SEXP arguments which are not Send. Do not route them through the worker thread; the trampolines bridge from C straight back into safe Rust on the main thread, with panic / longjmp handling per the chosen guard mode.

Enums

RBase

Base type for ALTREP vectors.

Statics

REGISTERED_CLASS_NAMES 🔒

Records every ALTREP class name registered during package_init().

Traits

AltrepClass

Trait implemented by ALTREP classes via #[miniextendr].

RegisterAltrep

Registration trait: implemented per type by the macro on struct items.

Functions

assert_altrep_class_uniqueness

Assert that all registered ALTREP class names are unique.

make_class_by_base^⚠

Create an ALTREP class handle based on the runtime base type.

validate_altrep_class

Validate that an ALTREP class handle was successfully created.