bitflags::bitflags! [−] [src]

macro_rules! bitflags {
    ($(#[$attr:meta])* flags $BitFlags:ident: $T:ty {
        $($(#[$Flag_attr:meta])* const $Flag:ident = $value:expr),+
    }) => { ... };
    ($(#[$attr:meta])* flags $BitFlags:ident: $T:ty {
        $($(#[$Flag_attr:meta])* const $Flag:ident = $value:expr),+,
    }) => { ... };
}

The bitflags! macro generates a struct that holds a set of C-style bitmask flags. It is useful for creating typesafe wrappers for C APIs.

The flags should only be defined for integer types, otherwise unexpected type errors may occur at compile time.

Example

#[macro_use]
extern crate bitflags;

bitflags! {
    flags Flags: u32 {
        const FLAG_A       = 0b00000001,
        const FLAG_B       = 0b00000010,
        const FLAG_C       = 0b00000100,
        const FLAG_ABC     = FLAG_A.bits
                           | FLAG_B.bits
                           | FLAG_C.bits,
    }
}

fn main() {
    let e1 = FLAG_A | FLAG_C;
    let e2 = FLAG_B | FLAG_C;
    assert!((e1 | e2) == FLAG_ABC);   // union
    assert!((e1 & e2) == FLAG_C);     // intersection
    assert!((e1 - e2) == FLAG_A);     // set difference
    assert!(!e2 == FLAG_A);           // set complement
}

The generated structs can also be extended with type and trait implementations:

#[macro_use]
extern crate bitflags;

use std::fmt;

bitflags! {
    flags Flags: u32 {
        const FLAG_A   = 0b00000001,
        const FLAG_B   = 0b00000010,
    }
}

impl Flags {
    pub fn clear(&mut self) {
        self.bits = 0;  // The `bits` field can be accessed from within the
                        // same module where the `bitflags!` macro was invoked.
    }
}

impl fmt::Display for Flags {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "hi!")
    }
}

fn main() {
    let mut flags = FLAG_A | FLAG_B;
    flags.clear();
    assert!(flags.is_empty());
    assert_eq!(format!("{}", flags), "hi!");
    assert_eq!(format!("{:?}", FLAG_A | FLAG_B), "FLAG_A | FLAG_B");
    assert_eq!(format!("{:?}", FLAG_B), "FLAG_B");
}

Attributes

Attributes can be attached to the generated struct by placing them before the flags keyword.

Trait implementations

The Copy, Clone, PartialEq, Eq, PartialOrd, Ord and Hash traits automatically derived for the struct using the derive attribute. Additional traits can be derived by providing an explicit derive attribute on flags.

The FromIterator trait is implemented for the struct, too, calculating the union of the instances of the struct iterated over.

The Debug trait is also implemented by displaying the bits value of the internal struct.

Operators

The following operator traits are implemented for the generated struct:

Methods

The following methods are defined for the generated struct: