Function dollar_extract 

pub unsafe fn dollar_extract(target: SEXP, name: &str) -> Result<SEXP, String>

Build and evaluate target$name — the R $ extraction operator.

This is a convenience wrapper that avoids hand-rolling Rf_install("$") + Rf_lang3(...) + R_tryEvalSilent(...) ladders. Equivalent to:

RCall::new("$")
    .arg(target)
    .arg(SEXP::scalar_string_from_str(name))
    .eval_base()

but uses the more direct LANGSXP form internally and protects all intermediate allocations via RAII.

Safety

• Must be called from the R main thread.
• target must be a valid SEXP (typically a list, environment, or S4 object that supports $ extraction).

Returns

• Ok(SEXP) with the extracted value (unprotected — caller should protect if needed).
• Err(String) with the R error message if $ extraction fails or the evaluation errors.