std::iter

Trait Step

pub trait Step:
    Sized
    + Clone
    + PartialOrd {
    // Required methods
    fn steps_between(start: &Self, end: &Self) -> (usize, Option<usize>);
    fn forward_checked(start: Self, count: usize) -> Option<Self>;
    fn backward_checked(start: Self, count: usize) -> Option<Self>;

    // Provided methods
    fn forward(start: Self, count: usize) -> Self { ... }
    unsafe fn forward_unchecked(start: Self, count: usize) -> Self { ... }
    fn backward(start: Self, count: usize) -> Self { ... }
    unsafe fn backward_unchecked(start: Self, count: usize) -> Self { ... }
}

🔬This is a nightly-only experimental API. (step_trait #42168)

Expand description

Objects that have a notion of successor and predecessor operations.

The successor operation moves towards values that compare greater. The predecessor operation moves towards values that compare lesser.

Required Methods§

fn steps_between(start: &Self, end: &Self) -> (usize, Option<usize>)

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the bounds on the number of successor steps required to get from start to end like Iterator::size_hint().

Returns (usize::MAX, None) if the number of steps would overflow usize, or is infinite.

§Invariants

For any a, b, and n:

steps_between(&a, &b) == (n, Some(n)) if and only if Step::forward_checked(&a, n) == Some(b)
steps_between(&a, &b) == (n, Some(n)) if and only if Step::backward_checked(&b, n) == Some(a)
steps_between(&a, &b) == (n, Some(n)) only if a <= b
- Corollary: steps_between(&a, &b) == (0, Some(0)) if and only if a == b
steps_between(&a, &b) == (0, None) if a > b

fn forward_checked(start: Self, count: usize) -> Option<Self>

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the successor of self count times.

If this would overflow the range of values supported by Self, returns None.

§Invariants

For any a, n, and m:

Step::forward_checked(a, n).and_then(|x| Step::forward_checked(x, m)) == Step::forward_checked(a, m).and_then(|x| Step::forward_checked(x, n))
Step::forward_checked(a, n).and_then(|x| Step::forward_checked(x, m)) == try { Step::forward_checked(a, n.checked_add(m)) }

For any a and n:

Step::forward_checked(a, n) == (0..n).try_fold(a, |x, _| Step::forward_checked(&x, 1))
- Corollary: Step::forward_checked(a, 0) == Some(a)

fn backward_checked(start: Self, count: usize) -> Option<Self>

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the predecessor of self count times.

If this would overflow the range of values supported by Self, returns None.

§Invariants

For any a, n, and m:

Step::backward_checked(a, n).and_then(|x| Step::backward_checked(x, m)) == n.checked_add(m).and_then(|x| Step::backward_checked(a, x))
Step::backward_checked(a, n).and_then(|x| Step::backward_checked(x, m)) == try { Step::backward_checked(a, n.checked_add(m)?) }

For any a and n:

Step::backward_checked(a, n) == (0..n).try_fold(a, |x, _| Step::backward_checked(x, 1))
- Corollary: Step::backward_checked(a, 0) == Some(a)

Provided Methods§

fn forward(start: Self, count: usize) -> Self

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the successor of self count times.

If this would overflow the range of values supported by Self, this function is allowed to panic, wrap, or saturate. The suggested behavior is to panic when debug assertions are enabled, and to wrap or saturate otherwise.

Unsafe code should not rely on the correctness of behavior after overflow.

§Invariants

For any a, n, and m, where no overflow occurs:

Step::forward(Step::forward(a, n), m) == Step::forward(a, n + m)

For any a and n, where no overflow occurs:

Step::forward_checked(a, n) == Some(Step::forward(a, n))
Step::forward(a, n) == (0..n).fold(a, |x, _| Step::forward(x, 1))
- Corollary: Step::forward(a, 0) == a
Step::forward(a, n) >= a
Step::backward(Step::forward(a, n), n) == a

unsafe fn forward_unchecked(start: Self, count: usize) -> Self

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the successor of self count times.

§Safety

It is undefined behavior for this operation to overflow the range of values supported by Self. If you cannot guarantee that this will not overflow, use forward or forward_checked instead.

§Invariants

For any a:

if there exists b such that b > a, it is safe to call Step::forward_unchecked(a, 1)
if there exists b, n such that steps_between(&a, &b) == Some(n), it is safe to call Step::forward_unchecked(a, m) for any m <= n.
- Corollary: Step::forward_unchecked(a, 0) is always safe.

For any a and n, where no overflow occurs:

Step::forward_unchecked(a, n) is equivalent to Step::forward(a, n)

fn backward(start: Self, count: usize) -> Self

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the predecessor of self count times.

If this would overflow the range of values supported by Self, this function is allowed to panic, wrap, or saturate. The suggested behavior is to panic when debug assertions are enabled, and to wrap or saturate otherwise.

Unsafe code should not rely on the correctness of behavior after overflow.

§Invariants

For any a, n, and m, where no overflow occurs:

Step::backward(Step::backward(a, n), m) == Step::backward(a, n + m)

For any a and n, where no overflow occurs:

Step::backward_checked(a, n) == Some(Step::backward(a, n))
Step::backward(a, n) == (0..n).fold(a, |x, _| Step::backward(x, 1))
- Corollary: Step::backward(a, 0) == a
Step::backward(a, n) <= a
Step::forward(Step::backward(a, n), n) == a

unsafe fn backward_unchecked(start: Self, count: usize) -> Self

🔬This is a nightly-only experimental API. (step_trait #42168)

Returns the value that would be obtained by taking the predecessor of self count times.

§Safety

It is undefined behavior for this operation to overflow the range of values supported by Self. If you cannot guarantee that this will not overflow, use backward or backward_checked instead.

§Invariants

For any a:

if there exists b such that b < a, it is safe to call Step::backward_unchecked(a, 1)
if there exists b, n such that steps_between(&b, &a) == (n, Some(n)), it is safe to call Step::backward_unchecked(a, m) for any m <= n.
- Corollary: Step::backward_unchecked(a, 0) is always safe.

For any a and n, where no overflow occurs:

Step::backward_unchecked(a, n) is equivalent to Step::backward(a, n)

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors§

§

Step

Trait Step Copy item path

Required Methods§

fn steps_between(start: &Self, end: &Self) -> (usize, Option<usize>)

§Invariants

fn forward_checked(start: Self, count: usize) -> Option<Self>

§Invariants

fn backward_checked(start: Self, count: usize) -> Option<Self>

§Invariants

Provided Methods§

fn forward(start: Self, count: usize) -> Self

§Invariants

unsafe fn forward_unchecked(start: Self, count: usize) -> Self

§Safety

§Invariants

fn backward(start: Self, count: usize) -> Self

§Invariants

unsafe fn backward_unchecked(start: Self, count: usize) -> Self

§Safety

§Invariants

Dyn Compatibility§

Implementors§

impl Step for AsciiChar

impl Step for char

impl Step for i8

impl Step for i16

impl Step for i32

impl Step for i64

impl Step for i128

impl Step for isize

impl Step for u8

impl Step for u16

impl Step for u32

impl Step for u64

impl Step for u128

impl Step for usize

impl Step for Ipv4Addr

impl Step for Ipv6Addr

Trait Step