Struct BitIndex 

pub struct BitIndex<T> { /* private fields */ }

Proof that a value is a valid bit index for T (0 <= index < T::BITS), so a shift by it can’t overflow, panic, or hit the “shift >= BITS” UB.

Like PowerOfTwo, the rep is the u32 index (never T), so the proof is Copy regardless of T; consuming ops live in BitIndexOps (signed and unsigned). No constant-time constructor — shift amounts are public.

use const_num_traits::{BitIndex, BitIndexOps};

let i = BitIndex::<u8>::new(3).unwrap();
assert_eq!(1u8.shl_index(i), 8);
assert_eq!(0x80u8.shr_index(i), 0x10);
assert!(BitIndex::<u8>::new(8).is_none()); // == BITS, rejected

Implementations

impl<T> BitIndex<T>

pub const unsafe fn from_u32_unchecked(index: u32) -> Self

Constructs the proof directly from an index, without checking.

Safety

index must be < T::BITS; otherwise the consuming shifts are undefined / panic.

pub const fn get(self) -> u32

The proven index. Free (no recompute).

impl<T> BitIndex<T>

pub fn new_checked(index: u32) -> Option<Self>

where T: PrimBits,

Safe constructor for any PrimBits carrier, not just the primitives: Some iff index < T::BITS. The per-primitive new stays the const fast path.

impl BitIndex<u8>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<u16>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<u32>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<u64>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

Examples found in repository

examples/typestates.rs (line 43)

fn bit_index() {
    let pos = BitIndex::<u64>::new(40).expect("40 < 64");
    assert_eq!((1u64).shl_index(pos), 1u64 << 40);
    assert_eq!((1u64 << 63).shr_index(pos), (1u64 << 63) >> 40);

    // out-of-range index is rejected at construction, not at the shift
    assert!(BitIndex::<u64>::new(64).is_none());
}

impl BitIndex<u128>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<usize>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<i8>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<i16>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<i32>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<i64>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<i128>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

impl BitIndex<isize>

pub const fn new(index: u32) -> Option<Self>

Checked constructor: Some iff index < <$t>::BITS.

Trait Implementations

impl<T> Clone for BitIndex<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Copy for BitIndex<T>

impl TryFrom<u32> for BitIndex<u8>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<u16>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<u32>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<u64>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<u128>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<usize>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<i8>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<i16>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<i32>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<i64>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<i128>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.

impl TryFrom<u32> for BitIndex<isize>

Checked construction from an index (< BITS); mirrors BitIndex::new. The source is the u32 index, not the carrier $t.

type Error = TypestateError

The type returned in the event of a conversion error.

fn try_from(index: u32) -> Result<Self, TypestateError>

Performs the conversion.