18 What is extendr?
Learn the different components of the extendr ecosystem.
extendr is a project that focuses on extending R with Rust. It is comprised of:
There is no single “extendr” library. Rather, that is the name of the project.
extendr-ffi
extendr-ffi defines the types and functions in R’s C API using Rust functions and types. As R’s C API changes, extendr-ffi is responsible for ensuring that packages are backwards compatible.
Fortunately, we will never have to touch this layer. Everything is built on top of this crate.
extendr-api
extendr-api is the high-level crate that is built upon extendr-ffi. It makes working with R types such as vectors feel fairly natural from a Rust perspective. It handles the oddities of garbage collection and everything else related to the FFI boundary.
We will spend the rest of the workshop using the extendr-api crate.
extendr-engine
The extendr-engine is focused on the opposite direction—calling R from Rust. It enables us to start an R process inside of Rust as well as execute R code in that R process. It can be used in creating Rust-based CLI tools that call R or whatever else your imagination can think up.
{rextendr}
On the R side exists {rextendr}. It is a {usethis}-like package for developing Rust-powered R packages.
It is primarily used to:
- scaffold R packages
- document Rust functions
- prepare packages for CRAN release
It also provide a knitr-engine which lets us include Rust in R Markdown documents.