Introduction

savvy is a simple R extension interface using Rust, like the extendr framework. The name “savvy” comes from the Japanese word “錆” (pronounced as sàbí), which means “Rust”.

With savvy, you can automatically generate R functions from Rust code. This is an example of what a savvy-powered function would look like:

Rust

use savvy::savvy;
use savvy::NotAvailableValue;   // for is_na() and na()

/// Convert to Upper-case
/// 
/// @param x A character vector.
/// @export
#[savvy]
fn to_upper(x: StringSexp) -> savvy::Result<savvy::Sexp> {
    // Use `Owned{type}Sexp` to allocate an R vector for output.
    let mut out = OwnedStringSexp::new(x.len())?;

    for (i, e) in x.iter().enumerate() {
        // To Rust, missing value is an ordinary value. In `&str`'s case, it's just "NA".
        // You have to use `.is_na()` method to distinguish the missing value.
        if e.is_na() {
            // Set the i-th element to NA
            out.set_na(i)?;
            continue;
        }

        let e_upper = e.to_uppercase();
        out.set_elt(i, e_upper.as_str())?;
    }

    out.into()
}

R

to_upper(c("a", "b", "c"))
#> [1] "A" "B" "C"

Examples

A toy example R package can be found in R-package/ directory.

Thanks

Savvy is not quite unique. This project is made possible by heavily taking inspiration from other great projects:

  • The basic idea is of course based on extendr. Savvy would not exist without extendr.
  • cpp11's "writable" concept influenced the design a lot. Also, I learned a lot from the great implementation such as the protection mechanism.
  • PyO3 made me realize that the FFI crate doesn't need to be a "sys" crate.