bitflag-attr

This is a proc-macro Rust crate that allows to turn a C-like enum into a bitflag structures with an API similar to bitfields crate.

You can use this crate to:

• provide more user-friendly bindings to C APIs where flags may or may not be fully known in advance.

You can't use this crate to:

• guarantee only bits corresponding to defined flags will ever be set. bitflag-attr allows access to the underlying bits type so arbitrary bits may be set.
• define bitfields. bitflag-attr only generates types where set bits denote the presence of some combination of flags.

Implemented traits

The macro requires that Clone and Copy are derived.

The macro will also implement some traits for bitwise operations and formatting.

• core::ops::Not
• core::ops::BitAnd
• core::ops::BitOr
• core::ops::BitXor
• core::ops::BitAndAssign
• core::ops::BitOrAssign
• core::ops::BitXorAssign
• core::ops::Sub
• core::ops::SubAssign
• core::fmt::Debug (This can be opt-out with the no_auto_debug)
• core::fmt::Binary
• core::fmt::UpperHex
• core::fmt::LowerHex
• core::fmt::Octal
• From

If the Debug trait is defined in the #[derive(...)] attribute. The macro will produce a custom implementation instead of the one Rust std produces

The macro also generate iterator types to iterate over the set flags, and for convenience also implement the following traits:

• core::iter::Extend
• core::iter::FromIterator
• core::iter::Iterator (for the type and reference)

There is a opt-in crate feature serde that generate a parsing error type and implements the traits:

• core::str::FromStr
• serde::Serialize
• serde::Deserialize

The custom implementation for Serialize and Deserialize will be generated only if those traits are in the #[derive(...)] attribute list (similar how the Debug works).

Note: This crate does not import/re-export serde traits, your project MUST have serde as dependency.

Example

Generate a flags structure:

use bitflag_attr::bitflag;

#[bitflag(u32)]
#[derive(Debug, Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Hash)]
enum Flags {
    /// The value `A`, at bit position `0`.
    A = 0b00000001,
    /// The value `B`, at bit position `1`.
    B = 0b00000010,
    /// The value `C`, at bit position `2`.
    C = 0b00000100,

    /// The combination of `A`, `B`, and `C`.
    ABC = A | B | C,
}

fn main() {
    let e1 = Flags::A | Flags::C;
    let e2 = Flags::B | Flags::C;
    assert_eq!((e1 | e2), Flags::ABC);   // union
    assert_eq!((e1 & e2), Flags::C);     // intersection
    assert_eq!((e1 - e2), Flags::A);     // set difference
    assert_eq!(!e2, Flags::A);           // set complement
}

If you don't want Debug trait to be generated, you can simply not define it on the derive attribute to the attribute.

use bitflag_attr::bitflag;

#[bitflag(u32)]
#[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Hash)]
enum Flags {
    /// The value `A`, at bit position `0`.
    A = 0b00000001,
    /// The value `B`, at bit position `1`.
    B = 0b00000010,
    /// The value `C`, at bit position `2`.
    C = 0b00000100,

    /// The combination of `A`, `B`, and `C`.
    ABC = A | B | C,
}

Rust Version Support

The minimum supported Rust version is documented in the Cargo.toml file. This may be bumped in minor releases as necessary.