Module match_arg_derive 

#[derive(MatchArg)] - Enum ↔ R String with match.arg Support

This module implements the #[derive(MatchArg)] macro which generates the MatchArg trait implementation for C-style enums, enabling automatic conversion between Rust enums and R character strings with partial matching.

Tradeoff

Without #[derive(MatchArg)], an enum-shaped argument lands in the Rust function as a raw String that you match on by hand — invalid values surface as Rust Err deep in the body, with no R-side defaulting and no partial matching. #[derive(MatchArg)] shifts that work to the wrapper boundary: the generated R wrapper picks up match.arg-style partial string matching against the enum’s variant list, fills in the first variant as the R-visible default, and rejects unknown values before the Rust function is even called. The variant list reaches the R side via a write-time placeholder (MX_MATCH_ARG_CHOICES) rather than a string baked into the proc macro, so adding a variant only requires re-running the build.

Usage

#[derive(Copy, Clone, MatchArg)]
enum Mode {
    Fast,
    Safe,
    Debug,
}

// Generates impl MatchArg for Mode, TryFromSexp for Mode, IntoR for Mode.

Attributes

• #[match_arg(rename = "name")] - Rename a variant’s choice string
• #[match_arg(rename_all = "snake_case")] - Rename all variants (snake_case, kebab-case, lower, upper)

Structs

MatchArgAttrs 🔒

Parsed #[match_arg(...)] attributes from an enum or variant.

Functions

derive_match_arg

Main entry point for #[derive(MatchArg)].

parse_match_arg_attrs 🔒

Parse #[match_arg(...)] attributes from a list of syn::Attribute.