How to Define and Manipulate Bit Flags in Rust with the bitflags Crate

Problem

You need to define and manipulate a set of bit flags in a Rust program, where each flag represents an independent boolean option.

Solution

Use the bitflags crate. Add bitflags = "2.6.0" to Cargo.toml, then invoke the bitflags! macro to declare a flag struct.

[dependencies]
bitflags = "2.6.0"

Define the flags:

use bitflags::bitflags;

bitflags! {
    struct Permissions: u32 {
        const READ    = 0b001;
        const WRITE   = 0b010;
        const EXECUTE = 0b100;
    }
}

Operate on them:

fn main() {
    let mut perms = Permissions::READ | Permissions::WRITE;

    assert!(perms.contains(Permissions::READ));
    assert!(!perms.contains(Permissions::EXECUTE));

    perms.insert(Permissions::EXECUTE);
    assert!(perms.contains(Permissions::EXECUTE));

    perms.remove(Permissions::WRITE);
    assert!(!perms.contains(Permissions::WRITE));
}

Discussion

The bitflags crate provides a convenient, type‑safe way to define and work with bit flags, useful in systems programming, file‑permission handling, and configuration options.

Structures generated by the bitflags! macro automatically implement traits such as Copy, Clone, PartialEq, Eq, PartialOrd, Ord, and Hash, making them easy to use in many contexts.

Common methods include: empty(): creates an empty flag set. all(): creates a set containing all flags. bits(): returns the underlying integer representation. from_bits(): creates a flag set from an integer. intersects(): checks for common flags.

Using bitflags makes code clearer and more type‑safe compared with raw integers and manual bitwise operations, reducing the chance of errors. Remember to assign each flag a distinct power‑of‑two value (1, 2, 4, 8, …) when defining them.