Function validate_altrep_class 

pub fn validate_altrep_class(
    cls: R_altrep_class_t,
    class_name: &CStr,
    base: RBase,
) -> R_altrep_class_t

Validate that an ALTREP class handle was successfully created.

Panics with a descriptive message if the class handle is null, indicating that R_make_alt*_class() failed during registration.

Also records the class name for later duplicate detection via assert_altrep_class_uniqueness.

Arguments

• cls - The class handle returned by R_make_alt*_class()
• class_name - The name of the ALTREP class (for diagnostics)
• base - The base R type (for diagnostics)