Macro bitflags::bitflags

macro_rules! bitflags {
    ($(#[$attr:meta])* pub 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),+
    }) => { ... };
    (@_impl flags $BitFlags:ident: $T:ty {
        $($(#[$Flag_attr:meta])* const $Flag:ident = $value:expr),+
    }) => { ... };
    ($(#[$attr:meta])* pub 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_eq!((e1 | e2), FLAG_ABC);   // union
    assert_eq!((e1 & e2), FLAG_C);     // intersection
    assert_eq!((e1 - e2), FLAG_A);     // set difference
    assert_eq!(!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");
}

Visibility

The generated struct and its associated flag constants are not exported out of the current module by default. A definition can be exported out of the current module by adding pub before flags:

#[macro_use]
extern crate bitflags;

mod example {
    bitflags! {
        pub flags Flags1: u32 {
            const FLAG_A   = 0b00000001,
        }
    }
    bitflags! {
        flags Flags2: u32 {
            const FLAG_B   = 0b00000010,
        }
    }
}

fn main() {
    let flag1 = example::FLAG_A;
    let flag2 = example::FLAG_B; // error: const `FLAG_B` is private
}

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 Extend and FromIterator traits are implemented for the struct, too: Extend adds the union of the instances of the struct iterated over, while FromIterator calculates the union.

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:

• BitOr and BitOrAssign: union
• BitAnd and BitAndAssign: intersection
• BitXor and BitXorAssign: toggle
• Sub and SubAssign: set difference
• Not: set complement

As long as the assignment operators are unstable rust feature they are only available with the crate feature assignment_ops enabled.

Methods

The following methods are defined for the generated struct:

• empty: an empty set of flags
• all: the set of all flags
• bits: the raw value of the flags currently stored
• from_bits: convert from underlying bit representation, unless that representation contains bits that do not correspond to a flag
• from_bits_truncate: convert from underlying bit representation, dropping any bits that do not correspond to flags
• is_empty: true if no flags are currently stored
• is_all: true if all flags are currently set
• intersects: true if there are flags common to both self and other
• contains: true all of the flags in other are contained within self
• insert: inserts the specified flags in-place
• remove: removes the specified flags in-place
• toggle: the specified flags will be inserted if not present, and removed if they are.