Module altrep_bridge 

Unsafe ALTREP trampolines and installers bridging safe traits to R’s C ABI.

This module is the seam between R’s C method tables and the safe traits in crate::altrep_traits. It provides:

• Generic extern "C-unwind" trampolines (t_length, t_dataptr, t_elt_*, …) that call into safe trait methods on T: Altrep.
• Installer functions (install_*) that register the trampolines with R based on the HAS_* const gates declared by the safe traits.

Non-allocating callbacks select T::GUARD at monomorphization time. Callbacks returning SEXP, Dataptr and string/list setters always use R_UnwindProtect: their generated bridges can allocate even when the underlying data provider is pure Rust.

Why a separate bridge module

R installs methods via raw extern "C-unwind" function pointers. To make impl Altrep for MyType ergonomic, we generate one trampoline per method once, generic over T: Altrep, that:

1. Recovers T’s monomorphization at the call site (no vtables).
2. Wraps the user callback in the per-type guard.
3. Hands the result back to R.

Users (and the #[derive(Altrep*)] macros) never call into this module directly — RegisterAltrep::get_or_init_class does.

Design

Trampolines are only installed when HAS_* is true. When false, the method is NOT installed with R, so R uses its own default behavior.

Macros

def_installer 🔒

Generate a family-specific installer function from a declarative spec.

Functions

guarded_altrep_call 🔒

Dispatch an ALTREP callback through the guard mode selected by T::GUARD.

guarded_altrep_r_call 🔒

Protect callbacks whose framework bridge may allocate in R, independently of the data provider’s guard choice for native reads.

guarded_altrep_sexp_call 🔒

Root an SEXP result before the guard allocates to signal deferred conditions.

install_base^⚠

Install base ALTREP methods (always installs length, conditionally installs optional).

install_cplx^⚠

Install complex-specific methods.

install_int^⚠

Install integer-specific methods.

install_lgl^⚠

Install logical-specific methods.

install_list^⚠

Install list-specific methods.

install_raw^⚠

Install raw-specific methods.

install_real^⚠

Install real-specific methods.

install_str^⚠

Install string-specific methods.

install_vec^⚠

Install vector-level methods.

t_coerce^⚠

Trampoline for Coerce method.

t_cplx_elt^⚠

Trampoline for complex Elt method.

t_cplx_get_region^⚠

Trampoline for complex Get_region method.

t_dataptr^⚠

Trampoline for Dataptr method.

t_dataptr_or_null^⚠

Trampoline for Dataptr_or_null method.

t_duplicate^⚠

Trampoline for Duplicate method.

t_duplicate_ex^⚠

Trampoline for DuplicateEX method (extended duplication).

t_extract_subset^⚠

Trampoline for Extract_subset method.

t_inspect^⚠

Trampoline for Inspect method.

t_int_elt^⚠

Trampoline for integer Elt method.

t_int_get_region^⚠

Trampoline for integer Get_region method.

t_int_is_sorted^⚠

Trampoline for integer Is_sorted method.

t_int_max^⚠

Trampoline for integer Max method.

t_int_min^⚠

Trampoline for integer Min method.

t_int_no_na^⚠

Trampoline for integer No_NA method.

t_int_sum^⚠

Trampoline for integer Sum method.

t_length^⚠

Trampoline for Length method.

t_lgl_elt^⚠

Trampoline for logical Elt method.

t_lgl_get_region^⚠

Trampoline for logical Get_region method.

t_lgl_is_sorted^⚠

Trampoline for logical Is_sorted method.

t_lgl_no_na^⚠

Trampoline for logical No_NA method.

t_lgl_sum^⚠

Trampoline for logical Sum method.

t_list_elt^⚠

Trampoline for list Elt method (REQUIRED for ALTLIST).

t_list_set_elt^⚠

Trampoline for list Set_elt method.

t_raw_elt^⚠

Trampoline for raw Elt method.

t_raw_get_region^⚠

Trampoline for raw Get_region method.

t_real_elt^⚠

Trampoline for real Elt method.

t_real_get_region^⚠

Trampoline for real Get_region method.

t_real_is_sorted^⚠

Trampoline for real Is_sorted method.

t_real_max^⚠

Trampoline for real Max method.

t_real_min^⚠

Trampoline for real Min method.

t_real_no_na^⚠

Trampoline for real No_NA method.

t_real_sum^⚠

Trampoline for real Sum method.

t_serialized_state^⚠

Trampoline for Serialized_state method.

t_str_elt^⚠

Trampoline for string Elt method (REQUIRED for ALTSTRING).

t_str_is_sorted^⚠

Trampoline for string Is_sorted method.

t_str_no_na^⚠

Trampoline for string No_NA method.

t_str_set_elt^⚠

Trampoline for string Set_elt method.

t_unserialize^⚠

Trampoline for Unserialize method.

t_unserialize_ex^⚠

Trampoline for UnserializeEX method (extended unserialization with attributes).