Module altrep_traits 

Safe, idiomatic ALTREP trait hierarchy mirroring R’s method tables.

Design: Required vs Optional Methods

Each ALTREP type family has:

• Required methods (no defaults) - compiler enforces implementation
• Optional methods with HAS_* const gating - defaults to false (not installed)

When HAS_* is false, the method is NOT installed with R, so R uses its own default behavior.

Required Methods by Type

Type	Required Methods
All	length
ALTSTRING	length + elt
ALTLIST	length + elt
Numeric types	length + (elt OR dataptr via HAS_*)

Enums

AltrepGuard

Controls the panic/error guard used around ALTREP trampoline callbacks.

Constants

KNOWN_UNSORTED

Known to be unsorted (KNOWN_UNSORTED in R).

NA_INTEGER

NA value for integers.

NA_LOGICAL

NA value for logical (same as integer in R).

NA_REAL

NA value for reals (IEEE NaN with R’s NA payload).

SORTED_DECR

Sorted in decreasing order, possibly with ties (SORTED_DECR in R).

SORTED_DECR_NA_1ST

Sorted in decreasing order, with NAs first (SORTED_DECR_NA_1ST in R).

SORTED_INCR

Sorted in increasing order, possibly with ties (SORTED_INCR in R).

SORTED_INCR_NA_1ST

Sorted in increasing order, with NAs first (SORTED_INCR_NA_1ST in R).

UNKNOWN_SORTEDNESS

Unknown sortedness value (INT_MIN in R).

Traits

AltComplex

Complex vector methods.

AltInteger

Integer vector methods.

AltList

List vector methods.

AltLogical

Logical vector methods.

AltRaw

Raw vector methods.

AltReal

Real vector methods.

AltString

String vector methods.

AltVec

Vector-level methods.

Altrep

Base ALTREP methods.