iot
iota
cargo install iota
iot

iota

Related constants in Rust: 1 << iota

by David Tolnay

0.2.2 (see all)License:MIT OR Apache-2.0
cargo install iota
Readme

1 << iota

github crates.io docs.rs build status

The iota! macro constructs a set of related constants.

[dependencies]
iota = "0.2"


use iota::iota;

iota! {
    const A: u8 = 1 << iota;
        , B
        , C
        , D
}

fn main() {
    assert_eq!(A, 1);
    assert_eq!(B, 2);
    assert_eq!(C, 4);
    assert_eq!(D, 8);
}

Within an iota! block, the iota variable is an untyped integer constant whose value begins at 0 and increments by 1 for every constant declared in the block.

use iota::iota;

iota! {
    const A: u8 = 1 << iota;
        , B

    const C: i32 = -1; // iota is not used but still incremented

    pub const D: u8 = iota * 2;
        , E
        , F
}

// `iota` begins again from 0 in this block
iota! {
    const G: usize = 1 << (iota + 10);
        , H
}

fn main() {
    assert_eq!(A, 1 << 0);
    assert_eq!(B, 1 << 1);

    assert_eq!(C, -1);

    assert_eq!(D, 3 * 2);
    assert_eq!(E, 4 * 2);
    assert_eq!(F, 5 * 2);

    assert_eq!(G, 1 << (0 + 10));
    assert_eq!(H, 1 << (1 + 10));
}

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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