Macro BitArr

macro_rules! BitArr {
    (for $len:expr, in $store:ty, $order:ty $(,)?) => { ... };
    (for $len:expr, in $store:ty $(,)?) => { ... };
    (for $len:expr) => { ... };
}

Bit-Array Type Definition

Because BitArray<T, O, const BITS: usize> is not expressible in stable Rust, this macro serves the purpose of creating a type definition that expands to a suitable BitArray. It creates the correct, rounded-up, BitArray to hold a requested number of bits in a requested set of ordering/storage parameters.

The macro takes a minimum number of bits to store, and an optional set of bit-order and bit-store type names, and creates a BitArray that satisfies the request. As this macro is only usable in type position, it is named with PascalCase rather than snake_case.

Examples

You must provide a bit-count; you may optionally provide a storage type, or a bit-ordering and a storage type, as subsequent arguments. When elided, the type parameters are set to the crate defaut type parameters of Lsb0 and usize.

use bitvec::prelude::*;
use core::cell::Cell;

let a: BitArr!(for 100) = BitArray::ZERO;
let b: BitArr!(for 100, in u32) = BitArray::<_>::ZERO;
let c: BitArr!(for 100, in Cell<u16>, Msb0) = BitArray::<_, _>::ZERO;

The length expression must be const. It may be a literal, a named const item, or a const expression, as long as it evaluates to a usize. The type arguments have no restrictions, as long as they are in-scope at the invocation site and are implementors of BitOrder and BitStore.