Crate atom_set 

atom_set

This library provides the AtomSet and DynAtomSet traits: the interface for a fixed set of keywords (“atoms”) which a lexer or parser matches ASCII case-insensitively, and stores as a small integer rather than a string.

An atom set is an enum. Each variant is one keyword, the #[default] variant is the empty atom which stands in for any unrecognised keyword, and the discriminant is the bit representation the token stores:

use atom_set::AtomSet;
use derive_atom_set::AtomSet as DeriveAtomSet;

#[derive(Debug, Default, Copy, Clone, PartialEq, DeriveAtomSet)]
pub enum Units {
    #[default]
    _None,
    Px,
    Rem,
    #[atom("%")]
    Percent,
}

assert_eq!(Units::from_str("PX"), Units::Px);
assert_eq!(Units::Rem.to_str(), "rem");
assert_eq!(Units::from_str("furlong"), Units::_None);
assert_eq!(Units::from_bits(Units::Percent.as_bits()), Units::Percent);

Write the impl with derive_atom_set, which generates lookup code specialised to the keyword lengths in the set. Hand written impls must keep AtomSet::from_str and AtomSet::to_str round-tripping, and must map the #[default] variant to the empty string.

DynAtomSet is the object-safe form. It exchanges bits and &'static str instead of Self, so a lexer can hold &'static dyn DynAtomSet and stay generic over the language it lexes. A blanket impl covers every AtomSet, so implementing it by hand is not required.

Part of csskit

This crate is part of csskit, a comprehensive CSS tool chain.

License

MIT

Traits

AtomSet

Usage with #[derive(AtomSet)]

DynAtomSet

Object-safe version of AtomSet for use with trait objects. This trait mirrors the functionality of AtomSet but is compatible with dyn trait objects.