grw_derive

Procedural macros for the GRW graph rewriting library.

This crate provides two macros used by grw for runtime type introspection and REPL integration. It is not intended to be used directly — it is re-exported through the grw crate.

#[derive(Val)]

Derives the Val trait on structs and #[repr(u8)] enums, providing:

• Field introspection — fields() returns field names, types, and byte offsets at runtime
• Layout hash — deterministic layout_hash() for binary compatibility checks (used by Graph::save/load)
• Size/alignment — size() and align() matching std::mem

use grw::Val;

#[derive(Val)]
struct Particle {
    x: f64,
    y: f64,
    mass: f32,
    active: bool,
}

// runtime field access
let fields = Particle::fields();
assert_eq!(fields[0].name, "x");
assert_eq!(fields.len(), 4);

// layout hash for persistence validation
let hash = Particle::layout_hash();
assert_ne!(hash, 0);

Supported field types: bool, i8–i64, u8–u64, f32, f64, String, nested Val structs, #[repr(u8)] enums.

Enums

#[derive(Val, Clone, Copy)]
#[repr(u8)]
enum Color { Red, Green, Blue }

// variants with discriminants are introspectable
let ft = Color::field_type();

#[grw::repl]

Attribute macro for impl blocks. Generates extern "C" wrappers and method metadata for REPL/JIT integration:

#[derive(Val)]
struct Point { x: f64, y: f64 }

#[grw::repl]
impl Point {
    fn distance(&self) -> f64 {
        (self.x * self.x + self.y * self.y).sqrt()
    }

    fn new(x: f64, y: f64) -> Self {
        Point { x, y }
    }
}

// methods are discoverable at runtime
let methods = Point::methods();
assert_eq!(methods[0].name, "distance");
assert!(!methods[0].is_static);

assert_eq!(methods[1].name, "new");
assert!(methods[1].is_static);

Supports:

• &self methods returning scalars (bool, i8–i64, u8–u64, f32, f64)
• Static methods (constructors, factories)
• Multi-parameter methods
• String return type (metadata only, fn_ptr is null — not callable via FFI)
• &mut self methods are silently skipped

License

Licensed under either of

• Apache License, Version 2.0
• MIT License

at your option.