Trait AltrepExtract 

pub trait AltrepExtract: Sized {
    // Required methods
    unsafe fn altrep_extract_ref(x: SEXP) -> &'static Self;
    unsafe fn altrep_extract_mut(x: SEXP) -> &'static mut Self;
}

How to extract a reference to Self from an ALTREP SEXP’s data1 slot.

The default implementation (for types that implement TypedExternal) extracts via ExternalPtr<T> downcast from data1. Power users who want native SEXP storage can implement this trait manually.

Safety

Implementations must ensure that the returned references are valid for the duration of the ALTREP callback (i.e., the SEXP is protected by R’s GC).

Panics

The blanket implementation panics if ExternalPtr extraction fails (type mismatch, null pointer, etc.). This is a programmer error, not a runtime condition. Callers must ensure the ALTREP SEXP was created with the correct data type. The panic is caught by the ALTREP guard (RustUnwind or RUnwind) and converted to an R error. Using AltrepGuard::Unsafe with a type that can fail extraction is unsound.

Required Methods

unsafe fn altrep_extract_ref(x: SEXP) -> &'static Self

Extract a shared reference from the ALTREP data1 slot.

Safety

• x must be a valid ALTREP SEXP whose data1 holds data of type Self
• Must be called from R’s main thread

unsafe fn altrep_extract_mut(x: SEXP) -> &'static mut Self

Extract a mutable reference from the ALTREP data1 slot.

Safety

• x must be a valid ALTREP SEXP whose data1 holds data of type Self
• Must be called from R’s main thread
• The caller must ensure no other references to the data exist

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl<T: TypedExternal> AltrepExtract for T

Blanket implementation for types stored in ExternalPtr (the common case).

This is the default storage strategy: data1 is an EXTPTRSXP wrapping a Box<Box<dyn Any>> that downcasts to &T.