Module altrep_derive 

Derive macros for ALTREP data traits.

These macros auto-implement AltrepLen and Alt*Data traits for simple field-based ALTREP types, reducing boilerplate for users.

Two paths: field-based vs manual

#[derive(AltrepInteger)] (and the Real / Logical / Raw / String / Complex / List variants) drive one of two code paths:

1. Field-based (default) — point the derive at struct fields that hold the vector length and a constant element value:

   #[derive(AltrepInteger)]
   #[altrep(len = "n", elt = "value", class = "Repeat")]
   struct Repeat { n: usize, value: i32 }

   The derive emits AltrepLen, AltIntegerData, Altrep, AltVec, RegisterAltrep, and the R_make_altinteger_class registration. No extra trait impls required.

2. Manual — #[altrep(manual)] suppresses AltrepLen / AltIntegerData generation so you can write the element-access logic yourself. The low-level trait impls (Altrep, AltVec, family methods, InferBase) are still emitted — #[altrep(no_lowlevel)] is the additional escape hatch when you also want to control Altrep / AltVec directly.

Pick by what your data looks like: a finite buffer that fits in a struct field → field-based; a computed element (fibonacci(i)) → manual.

Guard mode attribute

The derive recognises #[altrep(unsafe)] / #[altrep(rust_unwind)] / #[altrep(r_unwind)] on the struct, which sets the runtime Altrep::GUARD const that the trampolines in altrep_bridge dispatch on. Default is r_unwind (safe for callbacks that call R APIs).

Derive validation rules

Several #[altrep(...)] options conflict; the derive rejects illegal combinations at compile time:

Option	Allowed on families	Conflicts with
subset	all atomic (integer, real, logical, raw, string, complex)	dataptr, list
dataptr	integer, real, logical, raw, string, complex	subset, list
serialize	all	(none)
manual	all	(none — turns off AltrepLen/Alt*Data generation)
no_lowlevel	all	(none — also suppresses the low-level trait impls)

The list family rejects dataptr and subset — list elements are arbitrary SEXPs, so there is no contiguous buffer to expose.

Structs

AltrepAttrs 🔒

Parsed #[altrep(...)] attributes controlling ALTREP derive code generation.

AltrepFamilyConfig 🔒

Per-family configuration controlling low-level code generation for an ALTREP type family.

Functions

derive_altrep_complex

Derive macro entry point for AltrepComplex.

derive_altrep_generic 🔒

Shared implementation for all non-list ALTREP derive macros.

derive_altrep_integer

Derive macro entry point for AltrepInteger.

derive_altrep_list

Derive macro entry point for AltrepList.

derive_altrep_logical

Derive macro entry point for AltrepLogical.

derive_altrep_raw

Derive macro entry point for AltrepRaw.

derive_altrep_real

Derive macro entry point for AltrepReal.

derive_altrep_string

Derive macro entry point for AltrepString.

generate_altrep_len 🔒

Generates an impl AltrepLen for T block that delegates to a named struct field.