Function extract_arg 

pub unsafe fn extract_arg<T>(
    argc: i32,
    argv: *const SEXP,
    index: usize,
    name: &str,
) -> T
where
    T: TryFromSexp,
    T::Error: Display,

Extract and convert an argument from argv with bounds checking.

Checks that index < argc before extracting, and provides a helpful error message if out of bounds.

Type Parameters

• T - Target Rust type (must implement TryFromSexp)

Arguments

• argc - Number of arguments
• argv - Pointer to argument array
• index - Index of argument to extract
• name - Name of argument (for error messages)

Returns

The converted argument value.

Safety

• argv must point to at least argc valid SEXPs
• Must be called on R’s main thread

Errors

Calls rf_error if:

• index >= argc (missing argument)
• Conversion fails

Example

// In a method shim for fn foo(&self, x: i32, y: String)
let x: i32 = unsafe { extract_arg(argc, argv, 0, "x") };
let y: String = unsafe { extract_arg(argc, argv, 1, "y") };