bitflags

bitflags generates struct types that behave like C-style bitflag sets via the bitflags! macro. With ~1.1 billion all-time downloads, it is one of the top three most-downloaded crates on crates.io and is used by the Rust compiler itself.

What it provides

• Bitwise operations (|, &, ^, !) on flag sets
• Iteration over set flags
• String parsing and formatting
• const-compatible construction
• Exhaustive flag definitions with named constants

Alternatives

enumflags2 uses real enum syntax with a #[bitflags] attribute instead of a macro, providing a type-level distinction between a single flag (YourEnum) and a flag set (BitFlags<YourEnum>). enumset creates compact bitset-backed sets with set algebra operations (union, intersection, difference). Both are viable but bitflags' dominance makes it the default. See rust-enum-crates.