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