1 << iota
===============
[
](https://github.com/dtolnay/iota)
[
](https://crates.io/crates/iota)
[
](https://docs.rs/iota)
[
](https://github.com/dtolnay/iota/actions?query=branch%3Amaster)
The `iota!` macro constructs a set of related constants.
```toml
[dependencies]
iota = "0.2"
```
```rust
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.
```rust
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.