Module conv 

Type Conversion Helpers for Method Shims

This module provides type conversion functions used by the generated method shims from #[miniextendr] traits. These functions wrap the existing TryFromSexp and IntoR traits with appropriate error handling.

Purpose

Method shims generated by #[miniextendr] traits need to:

1. Convert SEXP arguments to Rust types
2. Convert Rust return values to SEXP
3. Handle conversion errors gracefully (via R errors)

This module provides a uniform interface for these conversions.

Error Handling

Conversion errors raise R errors (via Rf_error), which unwinds back to R. This ensures that:

• Invalid arguments produce helpful error messages
• R’s error handling mechanism is used consistently
• No Rust panics escape to R

Thread Safety

All functions in this module must be called on R’s main thread, as they interact with R’s SEXP values and error handling.

Functions

check_arity^⚠

Check that the number of arguments matches expected arity.

extract_arg^⚠

Extract and convert an argument from argv with bounds checking.

from_sexp^⚠

Convert an R SEXP to a Rust type, aborting via Rf_error on failure.

nil^⚠

Return R’s NULL value.

rf_error^⚠

Raise an R error with the given message.

to_sexp^⚠

Convert a Rust value to an R SEXP.

try_from_sexp^⚠

Convert an R SEXP to a Rust type, returning a Result.