21  Package structure

Objective

Understand the directory structure of extendr-based R packages.

The basic structure of an extendr-based R package is like so:

.
├── DESCRIPTION
├── NAMESPACE
├── R
├── configure
├── configure.win
├── man
├── src
└── tools

• tools/, configure, and configure.win are used at package build and install time to ensure that Rust is avaialble.
  • primarily for R CMD check and CRAN appeasement

Compiled Code

R packages that have compile code must store the source in src/. The src/ directory has the structure:

.
├── Makevars
├── Makevars.in
├── Makevars.win.in
└── rust
    ├── Cargo.lock
    ├── Cargo.toml
    ├── src

• rust/ is a library crate that is linked to by R
• Makevars files builds the Rust library and links it to R

Rust libraries

Rust library crates have lib.rs instead of main.rs. There is no entrypoint that gets executed. Instead, we define functions, structs, enums, etc. that are used by the R package.