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Auto merge of #69659 - CAD97:step-rework-take-3, r=Amanieu

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Rework the std::iter::Step trait

Previous attempts: #43127 #62886 #68807
Tracking issue: #42168

This PR reworks the `Step` trait to be phrased in terms of the *successor* and *predecessor* operations. With this, `Step` hopefully has a consistent identity that can have a path towards stabilization. The proposed trait:

```rust
/// 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.
///
/// # Safety
///
/// This trait is `unsafe` because its implementation must be correct for
/// the safety of `unsafe trait TrustedLen` implementations, and the results
/// of using this trait can otherwise be trusted by `unsafe` code to be correct
/// and fulful the listed obligations.
pub unsafe trait Step: Clone + PartialOrd + Sized {
    /// Returns the number of *successor* steps required to get from `start` to `end`.
    ///
    /// Returns `None` if the number of steps would overflow `usize`
    /// (or is infinite, or if `end` would never be reached).
    ///
    /// # Invariants
    ///
    /// For any `a`, `b`, and `n`:
    ///
    /// * `steps_between(&a, &b) == Some(n)` if and only if `Step::forward(&a, n) == Some(b)`
    /// * `steps_between(&a, &b) == Some(n)` if and only if `Step::backward(&a, n) == Some(a)`
    /// * `steps_between(&a, &b) == Some(n)` only if `a <= b`
    ///   * Corollary: `steps_between(&a, &b) == Some(0)` if and only if `a == b`
    ///   * Note that `a <= b` does _not_ imply `steps_between(&a, &b) != None`;
    ///     this is the case wheen it would require more than `usize::MAX` steps to get to `b`
    /// * `steps_between(&a, &b) == None` if `a > b`
    fn steps_between(start: &Self, end: &Self) -> Option<usize>;

    /// 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))`
    ///
    /// For any `a`, `n`, and `m` where `n + m` does not overflow:
    ///
    /// * `Step::forward_checked(a, n).and_then(|x| Step::forward_checked(x, m)) == Step::forward_checked(a, n + 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 forward_checked(start: Self, count: usize) -> Option<Self>;

    /// 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`
    fn forward(start: Self, count: usize) -> Self {
        Step::forward_checked(start, count).expect("overflow in `Step::forward`")
    }

    /// 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`.
    ///
    /// For any `a` and `n`, where no overflow occurs:
    ///
    /// * `Step::forward_unchecked(a, n)` is equivalent to `Step::forward(a, n)`
    #[unstable(feature = "unchecked_math", reason = "niche optimization path", issue = "none")]
    unsafe fn forward_unchecked(start: Self, count: usize) -> Self {
        Step::forward(start, count)
    }

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

    /// 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`
    fn backward(start: Self, count: usize) -> Self {
        Step::backward_checked(start, count).expect("overflow in `Step::backward`")
    }

    /// 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) == Some(n)`,
    ///   it is safe to call `Step::backward_unchecked(a, m)` for any `m <= n`.
    ///
    /// For any `a` and `n`, where no overflow occurs:
    ///
    /// * `Step::backward_unchecked(a, n)` is equivalent to `Step::backward(a, n)`
    #[unstable(feature = "unchecked_math", reason = "niche optimization path", issue = "none")]
    unsafe fn backward_unchecked(start: Self, count: usize) -> Self {
        Step::backward(start, count)
    }
}
```

Note that all of these are associated functions and not callable via method syntax; the calling syntax is always `Step::forward(start, n)`. This version of the trait additionally changes the stepping functions to talk their arguments by value.

As opposed to previous attempts which provided a "step by one" method directly, this version of the trait only exposes "step by n". There are a few reasons for this:

- `Range*`, the primary consumer of `Step`, assumes that the "step by n" operation is cheap. If a single step function is provided, it will be a lot more enticing to implement "step by n" as n repeated calls to "step by one". While this is not strictly incorrect, this behavior would be surprising for anyone used to using `Range<{primitive integer}>`.
- With a trivial default impl, this can be easily added backwards-compatibly later.
- The debug-wrapping "step by n" needs to exist for `RangeFrom` to be consistent between "step by n" and "step by one" operation. (Note: the behavior is not changed by this PR, but making the behavior consistent is made tenable by this PR.)

Three "kinds" of step are provided: `_checked`, which returns an `Option` indicating attempted overflow; (unsuffixed), which provides "safe overflow" behavior (is allowed to panic, wrap, or saturate, depending on what is most convenient for a given type); and `_unchecked`, which is a version which assumes overflow does not happen.

Review is appreciated to check that:

- The invariants as described on the `Step` functions are enough to specify the "common sense" consistency for successor/predecessor.
- Implementation of `Step` functions is correct in the face of overflow and the edges of representable integers.
- Added tests of `Step` functions are asserting the correct behavior (and not just the implemented behavior).
This commit is contained in:
bors 2020-05-15 11:24:50 +00:00
commit ed084b0b83
6 changed files with 632 additions and 258 deletions
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608
src/libcore/iter/range.rs
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@ -4,47 +4,182 @@ use crate::ops::{self, Add, Sub, Try};
use super::{FusedIterator, TrustedLen}; use super::{FusedIterator, TrustedLen};
/// Objects that can be stepped over in both directions. /// Objects that have a notion of *successor* and *predecessor* operations.
/// ///
/// The `steps_between` function provides a way to efficiently compare /// The *successor* operation moves towards values that compare greater.
/// two `Step` objects. /// The *predecessor* operation moves towards values that compare lesser.
#[unstable( ///
feature = "step_trait", /// # Safety
reason = "likely to be replaced by finer-grained traits", ///
issue = "42168" /// This trait is `unsafe` because its implementation must be correct for
)] /// the safety of `unsafe trait TrustedLen` implementations, and the results
pub trait Step: Clone + PartialOrd + Sized { /// of using this trait can otherwise be trusted by `unsafe` code to be correct
/// Returns the number of steps between two step objects. The count is /// and fulfill the listed obligations.
/// inclusive of `start` and exclusive of `end`. #[unstable(feature = "step_trait", reason = "recently redesigned", issue = "42168")]
pub unsafe trait Step: Clone + PartialOrd + Sized {
/// Returns the number of *successor* steps required to get from `start` to `end`.
/// ///
/// Returns `None` if it is not possible to calculate `steps_between` /// Returns `None` if the number of steps would overflow `usize`
/// without overflow. /// (or is infinite, or if `end` would never be reached).
///
/// # Invariants
///
/// For any `a`, `b`, and `n`:
///
/// * `steps_between(&a, &b) == Some(n)` if and only if `Step::forward_checked(&a, n) == Some(b)`
/// * `steps_between(&a, &b) == Some(n)` if and only if `Step::backward_checked(&a, n) == Some(a)`
/// * `steps_between(&a, &b) == Some(n)` only if `a <= b`
/// * Corollary: `steps_between(&a, &b) == Some(0)` if and only if `a == b`
/// * Note that `a <= b` does _not_ imply `steps_between(&a, &b) != None`;
/// this is the case wheen it would require more than `usize::MAX` steps to get to `b`
/// * `steps_between(&a, &b) == None` if `a > b`
fn steps_between(start: &Self, end: &Self) -> Option<usize>; fn steps_between(start: &Self, end: &Self) -> Option<usize>;
/// Replaces this step with `1`, returning a clone of itself. /// Returns the value that would be obtained by taking the *successor*
/// of `self` `count` times.
/// ///
/// The output of this method should always be greater than the output of replace_zero. /// If this would overflow the range of values supported by `Self`, returns `None`.
fn replace_one(&mut self) -> Self;
/// Replaces this step with `0`, returning a clone of itself.
/// ///
/// The output of this method should always be less than the output of replace_one. /// # Invariants
fn replace_zero(&mut self) -> Self; ///
/// 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))`
///
/// For any `a`, `n`, and `m` where `n + m` does not overflow:
///
/// * `Step::forward_checked(a, n).and_then(|x| Step::forward_checked(x, m)) == Step::forward_checked(a, n + 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)`
#[unstable(feature = "step_trait_ext", reason = "recently added", issue = "42168")]
fn forward_checked(start: Self, count: usize) -> Option<Self>;
/// Adds one to this step, returning the result. /// Returns the value that would be obtained by taking the *successor*
fn add_one(&self) -> Self; /// 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`
#[unstable(feature = "step_trait_ext", reason = "recently added", issue = "42168")]
fn forward(start: Self, count: usize) -> Self {
Step::forward_checked(start, count).expect("overflow in `Step::forward`")
}
/// Subtracts one to this step, returning the result. /// Returns the value that would be obtained by taking the *successor*
fn sub_one(&self) -> Self; /// 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`.
///
/// For any `a` and `n`, where no overflow occurs:
///
/// * `Step::forward_unchecked(a, n)` is equivalent to `Step::forward(a, n)`
#[unstable(feature = "unchecked_math", reason = "niche optimization path", issue = "none")]
unsafe fn forward_unchecked(start: Self, count: usize) -> Self {
Step::forward(start, count)
}
/// Adds a `usize`, returning `None` on overflow. /// Returns the value that would be obtained by taking the *successor*
fn add_usize(&self, n: usize) -> Option<Self>; /// 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)`
#[unstable(feature = "step_trait_ext", reason = "recently added", issue = "42168")]
fn backward_checked(start: Self, count: usize) -> Option<Self>;
/// Subtracts a `usize`, returning `None` on underflow. /// Returns the value that would be obtained by taking the *predecessor*
fn sub_usize(&self, n: usize) -> Option<Self> { /// of `self` `count` times.
// this default implementation makes the addition of `sub_usize` a non-breaking change ///
let _ = n; /// If this would overflow the range of values supported by `Self`,
unimplemented!() /// 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`
#[unstable(feature = "step_trait_ext", reason = "recently added", issue = "42168")]
fn backward(start: Self, count: usize) -> Self {
Step::backward_checked(start, count).expect("overflow in `Step::backward`")
}
/// 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) == Some(n)`,
/// it is safe to call `Step::backward_unchecked(a, m)` for any `m <= n`.
///
/// For any `a` and `n`, where no overflow occurs:
///
/// * `Step::backward_unchecked(a, n)` is equivalent to `Step::backward(a, n)`
#[unstable(feature = "unchecked_math", reason = "niche optimization path", issue = "none")]
unsafe fn backward_unchecked(start: Self, count: usize) -> Self {
Step::backward(start, count)
} }
} }
@ -52,127 +187,218 @@ pub trait Step: Clone + PartialOrd + Sized {
macro_rules! step_identical_methods { macro_rules! step_identical_methods {
() => { () => {
#[inline] #[inline]
fn replace_one(&mut self) -> Self { unsafe fn forward_unchecked(start: Self, n: usize) -> Self {
mem::replace(self, 1) start.unchecked_add(n as Self)
} }
#[inline] #[inline]
fn replace_zero(&mut self) -> Self { unsafe fn backward_unchecked(start: Self, n: usize) -> Self {
mem::replace(self, 0) start.unchecked_sub(n as Self)
} }
#[inline] #[inline]
fn add_one(&self) -> Self { fn forward(start: Self, n: usize) -> Self {
Add::add(*self, 1) // In debug builds, trigger a panic on overflow.
// This should optimize completely out in release builds.
if Self::forward_checked(start, n).is_none() {
let _ = Add::add(Self::MAX, 1);
}
// Do wrapping math to allow e.g. `Step::forward(-128i8, 255)`.
start.wrapping_add(n as Self)
} }
#[inline] #[inline]
fn sub_one(&self) -> Self { fn backward(start: Self, n: usize) -> Self {
Sub::sub(*self, 1) // In debug builds, trigger a panic on overflow.
// This should optimize completely out in release builds.
if Self::backward_checked(start, n).is_none() {
let _ = Sub::sub(Self::MIN, 1);
}
// Do wrapping math to allow e.g. `Step::backward(127i8, 255)`.
start.wrapping_sub(n as Self)
} }
}; };
} }
macro_rules! step_impl_unsigned { macro_rules! step_integer_impls {
($($t:ty)*) => ($( {
#[unstable(feature = "step_trait", narrower than or same width as usize:
reason = "likely to be replaced by finer-grained traits", $( [ $u_narrower:ident $i_narrower:ident ] ),+;
issue = "42168")] wider than usize:
impl Step for $t { $( [ $u_wider:ident $i_wider:ident ] ),+;
#[inline] } => {
fn steps_between(start: &$t, end: &$t) -> Option<usize> { $(
if *start < *end {
usize::try_from(*end - *start).ok()
} else {
Some(0)
}
}
#[inline]
#[allow(unreachable_patterns)] #[allow(unreachable_patterns)]
fn add_usize(&self, n: usize) -> Option<Self> { #[unstable(feature = "step_trait", reason = "recently redesigned", issue = "42168")]
match <$t>::try_from(n) { unsafe impl Step for $u_narrower {
Ok(n_as_t) => self.checked_add(n_as_t), step_identical_methods!();
Err(_) => None,
}
}
#[inline] #[inline]
#[allow(unreachable_patterns)] fn steps_between(start: &Self, end: &Self) -> Option<usize> {
fn sub_usize(&self, n: usize) -> Option<Self> { if *start <= *end {
match <$t>::try_from(n) { // This relies on $u_narrower <= usize
Ok(n_as_t) => self.checked_sub(n_as_t), Some((*end - *start) as usize)
Err(_) => None, } else {
} None
}
step_identical_methods!();
}
)*)
}
macro_rules! step_impl_signed {
($( [$t:ty : $unsigned:ty] )*) => ($(
#[unstable(feature = "step_trait",
reason = "likely to be replaced by finer-grained traits",
issue = "42168")]
impl Step for $t {
#[inline]
fn steps_between(start: &$t, end: &$t) -> Option<usize> {
if *start < *end {
// Use .wrapping_sub and cast to unsigned to compute the
// difference that may not fit inside the range of $t.
usize::try_from(end.wrapping_sub(*start) as $unsigned).ok()
} else {
Some(0)
}
}
#[inline]
#[allow(unreachable_patterns)]
fn add_usize(&self, n: usize) -> Option<Self> {
match <$unsigned>::try_from(n) {
Ok(n_as_unsigned) => {
// Wrapping in unsigned space handles cases like
// `-120_i8.add_usize(200) == Some(80_i8)`,
// even though 200_usize is out of range for i8.
let wrapped = (*self as $unsigned).wrapping_add(n_as_unsigned) as $t;
if wrapped >= *self {
Some(wrapped)
} else {
None // Addition overflowed
}
} }
Err(_) => None,
} }
}
#[inline] #[inline]
#[allow(unreachable_patterns)] fn forward_checked(start: Self, n: usize) -> Option<Self> {
fn sub_usize(&self, n: usize) -> Option<Self> { match Self::try_from(n) {
match <$unsigned>::try_from(n) { Ok(n) => start.checked_add(n),
Ok(n_as_unsigned) => { Err(_) => None, // if n is out of range, `unsigned_start + n` is too
// Wrapping in unsigned space handles cases like }
// `80_i8.sub_usize(200) == Some(-120_i8)`, }
// even though 200_usize is out of range for i8.
let wrapped = (*self as $unsigned).wrapping_sub(n_as_unsigned) as $t; #[inline]
if wrapped <= *self { fn backward_checked(start: Self, n: usize) -> Option<Self> {
Some(wrapped) match Self::try_from(n) {
} else { Ok(n) => start.checked_sub(n),
None // Subtraction underflowed Err(_) => None, // if n is out of range, `unsigned_start - n` is too
}
} }
Err(_) => None,
} }
} }
step_identical_methods!(); #[allow(unreachable_patterns)]
} #[unstable(feature = "step_trait", reason = "recently redesigned", issue = "42168")]
)*) unsafe impl Step for $i_narrower {
step_identical_methods!();
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
if *start <= *end {
// This relies on $i_narrower <= usize
//
// Casting to isize extends the width but preserves the sign.
// Use wrapping_sub in isize space and cast to usize to compute
// the difference that may not fit inside the range of isize.
Some((*end as isize).wrapping_sub(*start as isize) as usize)
} else {
None
}
}
#[inline]
fn forward_checked(start: Self, n: usize) -> Option<Self> {
match $u_narrower::try_from(n) {
Ok(n) => {
// Wrapping handles cases like
// `Step::forward(-120_i8, 200) == Some(80_i8)`,
// even though 200 is out of range for i8.
let wrapped = start.wrapping_add(n as Self);
if wrapped >= start {
Some(wrapped)
} else {
None // Addition overflowed
}
}
// If n is out of range of e.g. u8,
// then it is bigger than the entire range for i8 is wide
// so `any_i8 + n` necessarily overflows i8.
Err(_) => None,
}
}
#[inline]
fn backward_checked(start: Self, n: usize) -> Option<Self> {
match $u_narrower::try_from(n) {
Ok(n) => {
// Wrapping handles cases like
// `Step::forward(-120_i8, 200) == Some(80_i8)`,
// even though 200 is out of range for i8.
let wrapped = start.wrapping_sub(n as Self);
if wrapped <= start {
Some(wrapped)
} else {
None // Subtraction overflowed
}
}
// If n is out of range of e.g. u8,
// then it is bigger than the entire range for i8 is wide
// so `any_i8 - n` necessarily overflows i8.
Err(_) => None,
}
}
}
)+
$(
#[allow(unreachable_patterns)]
#[unstable(feature = "step_trait", reason = "recently redesigned", issue = "42168")]
unsafe impl Step for $u_wider {
step_identical_methods!();
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
if *start <= *end {
usize::try_from(*end - *start).ok()
} else {
None
}
}
#[inline]
fn forward_checked(start: Self, n: usize) -> Option<Self> {
start.checked_add(n as Self)
}
#[inline]
fn backward_checked(start: Self, n: usize) -> Option<Self> {
start.checked_sub(n as Self)
}
}
#[allow(unreachable_patterns)]
#[unstable(feature = "step_trait", reason = "recently redesigned", issue = "42168")]
unsafe impl Step for $i_wider {
step_identical_methods!();
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
if *start <= *end {
match end.checked_sub(*start) {
Some(result) => usize::try_from(result).ok(),
// If the difference is too big for e.g. i128,
// it's also gonna be too big for usize with fewer bits.
None => None,
}
} else {
None
}
}
#[inline]
fn forward_checked(start: Self, n: usize) -> Option<Self> {
start.checked_add(n as Self)
}
#[inline]
fn backward_checked(start: Self, n: usize) -> Option<Self> {
start.checked_sub(n as Self)
}
}
)+
};
} }
step_impl_unsigned!(usize u8 u16 u32 u64 u128); #[cfg(target_pointer_width = "64")]
step_impl_signed!([isize: usize][i8: u8][i16: u16]); step_integer_impls! {
step_impl_signed!([i32: u32][i64: u64][i128: u128]); narrower than or same width as usize: [u8 i8], [u16 i16], [u32 i32], [u64 i64], [usize isize];
wider than usize: [u128 i128];
}
#[cfg(target_pointer_width = "32")]
step_integer_impls! {
narrower than or same width as usize: [u8 i8], [u16 i16], [u32 i32], [usize isize];
wider than usize: [u64 i64], [u128 i128];
}
#[cfg(target_pointer_width = "16")]
step_integer_impls! {
narrower than or same width as usize: [u8 i8], [u16 i16], [usize isize];
wider than usize: [u32 i32], [u64 i64], [u128 i128];
}
macro_rules! range_exact_iter_impl { macro_rules! range_exact_iter_impl {
($($t:ty)*) => ($( ($($t:ty)*) => ($(
@ -188,20 +414,6 @@ macro_rules! range_incl_exact_iter_impl {
)*) )*)
} }
macro_rules! range_trusted_len_impl {
($($t:ty)*) => ($(
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl TrustedLen for ops::Range<$t> { }
)*)
}
macro_rules! range_incl_trusted_len_impl {
($($t:ty)*) => ($(
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl TrustedLen for ops::RangeInclusive<$t> { }
)*)
}
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step> Iterator for ops::Range<A> { impl<A: Step> Iterator for ops::Range<A> {
type Item = A; type Item = A;
@ -209,16 +421,12 @@ impl<A: Step> Iterator for ops::Range<A> {
#[inline] #[inline]
fn next(&mut self) -> Option<A> { fn next(&mut self) -> Option<A> {
if self.start < self.end { if self.start < self.end {
// We check for overflow here, even though it can't actually // SAFETY: just checked precondition
// happen. Adding this check does however help llvm vectorize loops // We use the unchecked version here, because
// for some ranges that don't get vectorized otherwise, // this helps LLVM vectorize loops for some ranges
// and this won't actually result in an extra check in an optimized build. // that don't get vectorized otherwise.
if let Some(mut n) = self.start.add_usize(1) { let n = unsafe { Step::forward_unchecked(self.start.clone(), 1) };
mem::swap(&mut n, &mut self.start); Some(mem::replace(&mut self.start, n))
Some(n)
} else {
None
}
} else { } else {
None None
} }
@ -226,17 +434,19 @@ impl<A: Step> Iterator for ops::Range<A> {
#[inline] #[inline]
fn size_hint(&self) -> (usize, Option<usize>) { fn size_hint(&self) -> (usize, Option<usize>) {
match Step::steps_between(&self.start, &self.end) { if self.start < self.end {
Some(hint) => (hint, Some(hint)), let hint = Step::steps_between(&self.start, &self.end);
None => (usize::MAX, None), (hint.unwrap_or(usize::MAX), hint)
} else {
(0, Some(0))
} }
} }
#[inline] #[inline]
fn nth(&mut self, n: usize) -> Option<A> { fn nth(&mut self, n: usize) -> Option<A> {
if let Some(plus_n) = self.start.add_usize(n) { if let Some(plus_n) = Step::forward_checked(self.start.clone(), n) {
if plus_n < self.end { if plus_n < self.end {
self.start = plus_n.add_one(); self.start = Step::forward(plus_n.clone(), 1);
return Some(plus_n); return Some(plus_n);
} }
} }
@ -262,25 +472,42 @@ impl<A: Step> Iterator for ops::Range<A> {
} }
// These macros generate `ExactSizeIterator` impls for various range types. // These macros generate `ExactSizeIterator` impls for various range types.
// Range<{u,i}64> and RangeInclusive<{u,i}{32,64,size}> are excluded
// because they cannot guarantee having a length <= usize::MAX, which is
// required by ExactSizeIterator.
range_exact_iter_impl!(usize u8 u16 u32 isize i8 i16 i32);
range_incl_exact_iter_impl!(u8 u16 i8 i16);
// These macros generate `TrustedLen` impls.
// //
// They need to guarantee that .size_hint() is either exact, or that // * `ExactSizeIterator::len` is required to always return an exact `usize`,
// the upper bound is None when it does not fit the type limits. // so no range can be longer than `usize::MAX`.
range_trusted_len_impl!(usize isize u8 i8 u16 i16 u32 i32 u64 i64 u128 i128); // * For integer types in `Range<_>` this is the case for types narrower than or as wide as `usize`.
range_incl_trusted_len_impl!(usize isize u8 i8 u16 i16 u32 i32 u64 i64 u128 i128); // For integer types in `RangeInclusive<_>`
// this is the case for types *strictly narrower* than `usize`
// since e.g. `(0..=u64::MAX).len()` would be `u64::MAX + 1`.
range_exact_iter_impl! {
usize u8 u16
isize i8 i16
// These are incorect per the reasoning above,
// but removing them would be a breaking change as they were stabilized in Rust 1.0.0.
// So e.g. `(0..66_000_u32).len()` for example will compile without error or warnings
// on 16-bit platforms, but continue to give a wrong result.
u32
i32
}
range_incl_exact_iter_impl! {
u8
i8
// These are incorect per the reasoning above,
// but removing them would be a breaking change as they were stabilized in Rust 1.26.0.
// So e.g. `(0..=u16::MAX).len()` for example will compile without error or warnings
// on 16-bit platforms, but continue to give a wrong result.
u16
i16
}
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step> DoubleEndedIterator for ops::Range<A> { impl<A: Step> DoubleEndedIterator for ops::Range<A> {
#[inline] #[inline]
fn next_back(&mut self) -> Option<A> { fn next_back(&mut self) -> Option<A> {
if self.start < self.end { if self.start < self.end {
self.end = self.end.sub_one(); self.end = Step::backward(self.end.clone(), 1);
Some(self.end.clone()) Some(self.end.clone())
} else { } else {
None None
@ -289,9 +516,9 @@ impl<A: Step> DoubleEndedIterator for ops::Range<A> {
#[inline] #[inline]
fn nth_back(&mut self, n: usize) -> Option<A> { fn nth_back(&mut self, n: usize) -> Option<A> {
if let Some(minus_n) = self.end.sub_usize(n) { if let Some(minus_n) = Step::backward_checked(self.end.clone(), n) {
if minus_n > self.start { if minus_n > self.start {
self.end = minus_n.sub_one(); self.end = Step::backward(minus_n, 1);
return Some(self.end.clone()); return Some(self.end.clone());
} }
} }
@ -301,6 +528,9 @@ impl<A: Step> DoubleEndedIterator for ops::Range<A> {
} }
} }
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A: Step> TrustedLen for ops::Range<A> {}
#[stable(feature = "fused", since = "1.26.0")] #[stable(feature = "fused", since = "1.26.0")]
impl<A: Step> FusedIterator for ops::Range<A> {} impl<A: Step> FusedIterator for ops::Range<A> {}
@ -310,9 +540,8 @@ impl<A: Step> Iterator for ops::RangeFrom<A> {
#[inline] #[inline]
fn next(&mut self) -> Option<A> { fn next(&mut self) -> Option<A> {
let mut n = self.start.add_one(); let n = Step::forward(self.start.clone(), 1);
mem::swap(&mut n, &mut self.start); Some(mem::replace(&mut self.start, n))
Some(n)
} }
#[inline] #[inline]
@ -322,8 +551,16 @@ impl<A: Step> Iterator for ops::RangeFrom<A> {
#[inline] #[inline]
fn nth(&mut self, n: usize) -> Option<A> { fn nth(&mut self, n: usize) -> Option<A> {
let plus_n = self.start.add_usize(n).expect("overflow in RangeFrom::nth"); // If we would jump over the maximum value, panic immediately.
self.start = plus_n.add_one(); // This is consistent with behavior before the Step redesign,
// even though it's inconsistent with n `next` calls.
// To get consistent behavior, change it to use `forward` instead.
// This change should go through FCP separately to the redesign, so is for now left as a
// FIXME: make this consistent
let plus_n =
Step::forward_checked(self.start.clone(), n).expect("overflow in RangeFrom::nth");
// The final step should always be debug-checked.
self.start = Step::forward(plus_n.clone(), 1);
Some(plus_n) Some(plus_n)
} }
} }
@ -345,7 +582,7 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
} }
let is_iterating = self.start < self.end; let is_iterating = self.start < self.end;
Some(if is_iterating { Some(if is_iterating {
let n = self.start.add_one(); let n = Step::forward(self.start.clone(), 1);
mem::replace(&mut self.start, n) mem::replace(&mut self.start, n)
} else { } else {
self.exhausted = true; self.exhausted = true;
@ -371,12 +608,12 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
return None; return None;
} }
if let Some(plus_n) = self.start.add_usize(n) { if let Some(plus_n) = Step::forward_checked(self.start.clone(), n) {
use crate::cmp::Ordering::*; use crate::cmp::Ordering::*;
match plus_n.partial_cmp(&self.end) { match plus_n.partial_cmp(&self.end) {
Some(Less) => { Some(Less) => {
self.start = plus_n.add_one(); self.start = Step::forward(plus_n.clone(), 1);
return Some(plus_n); return Some(plus_n);
} }
Some(Equal) => { Some(Equal) => {
@ -407,7 +644,7 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
let mut accum = init; let mut accum = init;
while self.start < self.end { while self.start < self.end {
let n = self.start.add_one(); let n = Step::forward(self.start.clone(), 1);
let n = mem::replace(&mut self.start, n); let n = mem::replace(&mut self.start, n);
accum = f(accum, n)?; accum = f(accum, n)?;
} }
@ -446,7 +683,7 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
} }
let is_iterating = self.start < self.end; let is_iterating = self.start < self.end;
Some(if is_iterating { Some(if is_iterating {
let n = self.end.sub_one(); let n = Step::backward(self.end.clone(), 1);
mem::replace(&mut self.end, n) mem::replace(&mut self.end, n)
} else { } else {
self.exhausted = true; self.exhausted = true;
@ -460,12 +697,12 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
return None; return None;
} }
if let Some(minus_n) = self.end.sub_usize(n) { if let Some(minus_n) = Step::backward_checked(self.end.clone(), n) {
use crate::cmp::Ordering::*; use crate::cmp::Ordering::*;
match minus_n.partial_cmp(&self.start) { match minus_n.partial_cmp(&self.start) {
Some(Greater) => { Some(Greater) => {
self.end = minus_n.sub_one(); self.end = Step::backward(minus_n.clone(), 1);
return Some(minus_n); return Some(minus_n);
} }
Some(Equal) => { Some(Equal) => {
@ -496,7 +733,7 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
let mut accum = init; let mut accum = init;
while self.start < self.end { while self.start < self.end {
let n = self.end.sub_one(); let n = Step::backward(self.end.clone(), 1);
let n = mem::replace(&mut self.end, n); let n = mem::replace(&mut self.end, n);
accum = f(accum, n)?; accum = f(accum, n)?;
} }
@ -511,5 +748,8 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
} }
} }
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A: Step> TrustedLen for ops::RangeInclusive<A> {}
#[stable(feature = "fused", since = "1.26.0")] #[stable(feature = "fused", since = "1.26.0")]
impl<A: Step> FusedIterator for ops::RangeInclusive<A> {} impl<A: Step> FusedIterator for ops::RangeInclusive<A> {}

102
src/libcore/num/mod.rs
View file

@ -749,6 +749,23 @@ $EndFeature, "
} }
} }
doc_comment! {
concat!("Unchecked integer addition. Computes `self + rhs, assuming overflow
cannot occur. This results in undefined behavior when `self + rhs > ", stringify!($SelfT),
"::max_value()` or `self + rhs < ", stringify!($SelfT), "::min_value()`."),
#[unstable(
feature = "unchecked_math",
reason = "niche optimization path",
issue = "none",
)]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub unsafe fn unchecked_add(self, rhs: Self) -> Self {
intrinsics::unchecked_add(self, rhs)
}
}
doc_comment! { doc_comment! {
concat!("Checked integer subtraction. Computes `self - rhs`, returning `None` if concat!("Checked integer subtraction. Computes `self - rhs`, returning `None` if
overflow occurred. overflow occurred.
@ -774,6 +791,23 @@ $EndFeature, "
} }
} }
doc_comment! {
concat!("Unchecked integer subtraction. Computes `self - rhs, assuming overflow
cannot occur. This results in undefined behavior when `self - rhs > ", stringify!($SelfT),
"::max_value()` or `self - rhs < ", stringify!($SelfT), "::min_value()`."),
#[unstable(
feature = "unchecked_math",
reason = "niche optimization path",
issue = "none",
)]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub unsafe fn unchecked_sub(self, rhs: Self) -> Self {
intrinsics::unchecked_sub(self, rhs)
}
}
doc_comment! { doc_comment! {
concat!("Checked integer multiplication. Computes `self * rhs`, returning `None` if concat!("Checked integer multiplication. Computes `self * rhs`, returning `None` if
overflow occurred. overflow occurred.
@ -799,6 +833,23 @@ $EndFeature, "
} }
} }
doc_comment! {
concat!("Unchecked integer multiplication. Computes `self * rhs, assuming overflow
cannot occur. This results in undefined behavior when `self * rhs > ", stringify!($SelfT),
"::max_value()` or `self * rhs < ", stringify!($SelfT), "::min_value()`."),
#[unstable(
feature = "unchecked_math",
reason = "niche optimization path",
issue = "none",
)]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub unsafe fn unchecked_mul(self, rhs: Self) -> Self {
intrinsics::unchecked_mul(self, rhs)
}
}
doc_comment! { doc_comment! {
concat!("Checked integer division. Computes `self / rhs`, returning `None` if `rhs == 0` concat!("Checked integer division. Computes `self / rhs`, returning `None` if `rhs == 0`
or the division results in overflow. or the division results in overflow.
@ -2936,6 +2987,23 @@ assert_eq!((", stringify!($SelfT), "::MAX - 2).checked_add(3), None);", $EndFeat
} }
} }
doc_comment! {
concat!("Unchecked integer addition. Computes `self + rhs, assuming overflow
cannot occur. This results in undefined behavior when `self + rhs > ", stringify!($SelfT),
"::max_value()` or `self + rhs < ", stringify!($SelfT), "::min_value()`."),
#[unstable(
feature = "unchecked_math",
reason = "niche optimization path",
issue = "none",
)]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub unsafe fn unchecked_add(self, rhs: Self) -> Self {
intrinsics::unchecked_add(self, rhs)
}
}
doc_comment! { doc_comment! {
concat!("Checked integer subtraction. Computes `self - rhs`, returning concat!("Checked integer subtraction. Computes `self - rhs`, returning
`None` if overflow occurred. `None` if overflow occurred.
@ -2959,6 +3027,23 @@ assert_eq!(0", stringify!($SelfT), ".checked_sub(1), None);", $EndFeature, "
} }
} }
doc_comment! {
concat!("Unchecked integer subtraction. Computes `self - rhs, assuming overflow
cannot occur. This results in undefined behavior when `self - rhs > ", stringify!($SelfT),
"::max_value()` or `self - rhs < ", stringify!($SelfT), "::min_value()`."),
#[unstable(
feature = "unchecked_math",
reason = "niche optimization path",
issue = "none",
)]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub unsafe fn unchecked_sub(self, rhs: Self) -> Self {
intrinsics::unchecked_sub(self, rhs)
}
}
doc_comment! { doc_comment! {
concat!("Checked integer multiplication. Computes `self * rhs`, returning concat!("Checked integer multiplication. Computes `self * rhs`, returning
`None` if overflow occurred. `None` if overflow occurred.
@ -2982,6 +3067,23 @@ assert_eq!(", stringify!($SelfT), "::MAX.checked_mul(2), None);", $EndFeature, "
} }
} }
doc_comment! {
concat!("Unchecked integer multiplication. Computes `self * rhs, assuming overflow
cannot occur. This results in undefined behavior when `self * rhs > ", stringify!($SelfT),
"::max_value()` or `self * rhs < ", stringify!($SelfT), "::min_value()`."),
#[unstable(
feature = "unchecked_math",
reason = "niche optimization path",
issue = "none",
)]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub unsafe fn unchecked_mul(self, rhs: Self) -> Self {
intrinsics::unchecked_mul(self, rhs)
}
}
doc_comment! { doc_comment! {
concat!("Checked integer division. Computes `self / rhs`, returning `None` concat!("Checked integer division. Computes `self / rhs`, returning `None`
if `rhs == 0`. if `rhs == 0`.

121
src/libcore/tests/iter.rs
View file

@ -2139,6 +2139,24 @@ fn test_range_inclusive_nth_back() {
assert_eq!(ExactSizeIterator::is_empty(&r), true); assert_eq!(ExactSizeIterator::is_empty(&r), true);
} }
#[test]
fn test_range_len() {
assert_eq!((0..10_u8).len(), 10);
assert_eq!((9..10_u8).len(), 1);
assert_eq!((10..10_u8).len(), 0);
assert_eq!((11..10_u8).len(), 0);
assert_eq!((100..10_u8).len(), 0);
}
#[test]
fn test_range_inclusive_len() {
assert_eq!((0..=10_u8).len(), 11);
assert_eq!((9..=10_u8).len(), 2);
assert_eq!((10..=10_u8).len(), 1);
assert_eq!((11..=10_u8).len(), 0);
assert_eq!((100..=10_u8).len(), 0);
}
#[test] #[test]
fn test_range_step() { fn test_range_step() {
#![allow(deprecated)] #![allow(deprecated)]
@ -2509,42 +2527,91 @@ fn test_chain_fold() {
} }
#[test] #[test]
fn test_step_replace_unsigned() { fn test_steps_between() {
let mut x = 4u32; assert_eq!(Step::steps_between(&20_u8, &200_u8), Some(180_usize));
let y = x.replace_zero(); assert_eq!(Step::steps_between(&-20_i8, &80_i8), Some(100_usize));
assert_eq!(x, 0); assert_eq!(Step::steps_between(&-120_i8, &80_i8), Some(200_usize));
assert_eq!(y, 4); assert_eq!(Step::steps_between(&20_u32, &4_000_100_u32), Some(4_000_080_usize));
assert_eq!(Step::steps_between(&-20_i32, &80_i32), Some(100_usize));
assert_eq!(Step::steps_between(&-2_000_030_i32, &2_000_050_i32), Some(4_000_080_usize));
x = 5; // Skip u64/i64 to avoid differences with 32-bit vs 64-bit platforms
let y = x.replace_one();
assert_eq!(x, 1); assert_eq!(Step::steps_between(&20_u128, &200_u128), Some(180_usize));
assert_eq!(y, 5); assert_eq!(Step::steps_between(&-20_i128, &80_i128), Some(100_usize));
if cfg!(target_pointer_width = "64") {
assert_eq!(Step::steps_between(&10_u128, &0x1_0000_0000_0000_0009_u128), Some(usize::MAX));
}
assert_eq!(Step::steps_between(&10_u128, &0x1_0000_0000_0000_000a_u128), None);
assert_eq!(Step::steps_between(&10_i128, &0x1_0000_0000_0000_000a_i128), None);
assert_eq!(
Step::steps_between(&-0x1_0000_0000_0000_0000_i128, &0x1_0000_0000_0000_0000_i128,),
None,
);
} }
#[test] #[test]
fn test_step_replace_signed() { fn test_step_forward() {
let mut x = 4i32; assert_eq!(Step::forward_checked(55_u8, 200_usize), Some(255_u8));
let y = x.replace_zero(); assert_eq!(Step::forward_checked(252_u8, 200_usize), None);
assert_eq!(x, 0); assert_eq!(Step::forward_checked(0_u8, 256_usize), None);
assert_eq!(y, 4); assert_eq!(Step::forward_checked(-110_i8, 200_usize), Some(90_i8));
assert_eq!(Step::forward_checked(-110_i8, 248_usize), None);
assert_eq!(Step::forward_checked(-126_i8, 256_usize), None);
x = 5; assert_eq!(Step::forward_checked(35_u16, 100_usize), Some(135_u16));
let y = x.replace_one(); assert_eq!(Step::forward_checked(35_u16, 65500_usize), Some(u16::MAX));
assert_eq!(x, 1); assert_eq!(Step::forward_checked(36_u16, 65500_usize), None);
assert_eq!(y, 5); assert_eq!(Step::forward_checked(-110_i16, 200_usize), Some(90_i16));
assert_eq!(Step::forward_checked(-20_030_i16, 50_050_usize), Some(30_020_i16));
assert_eq!(Step::forward_checked(-10_i16, 40_000_usize), None);
assert_eq!(Step::forward_checked(-10_i16, 70_000_usize), None);
assert_eq!(Step::forward_checked(10_u128, 70_000_usize), Some(70_010_u128));
assert_eq!(Step::forward_checked(10_i128, 70_030_usize), Some(70_040_i128));
assert_eq!(
Step::forward_checked(0xffff_ffff_ffff_ffff__ffff_ffff_ffff_ff00_u128, 0xff_usize),
Some(u128::MAX),
);
assert_eq!(
Step::forward_checked(0xffff_ffff_ffff_ffff__ffff_ffff_ffff_ff00_u128, 0x100_usize),
None
);
assert_eq!(
Step::forward_checked(0x7fff_ffff_ffff_ffff__ffff_ffff_ffff_ff00_i128, 0xff_usize),
Some(i128::MAX),
);
assert_eq!(
Step::forward_checked(0x7fff_ffff_ffff_ffff__ffff_ffff_ffff_ff00_i128, 0x100_usize),
None
);
} }
#[test] #[test]
fn test_step_replace_no_between() { fn test_step_backward() {
let mut x = 4u128; assert_eq!(Step::backward_checked(255_u8, 200_usize), Some(55_u8));
let y = x.replace_zero(); assert_eq!(Step::backward_checked(100_u8, 200_usize), None);
assert_eq!(x, 0); assert_eq!(Step::backward_checked(255_u8, 256_usize), None);
assert_eq!(y, 4); assert_eq!(Step::backward_checked(90_i8, 200_usize), Some(-110_i8));
assert_eq!(Step::backward_checked(110_i8, 248_usize), None);
assert_eq!(Step::backward_checked(127_i8, 256_usize), None);
x = 5; assert_eq!(Step::backward_checked(135_u16, 100_usize), Some(35_u16));
let y = x.replace_one(); assert_eq!(Step::backward_checked(u16::MAX, 65500_usize), Some(35_u16));
assert_eq!(x, 1); assert_eq!(Step::backward_checked(10_u16, 11_usize), None);
assert_eq!(y, 5); assert_eq!(Step::backward_checked(90_i16, 200_usize), Some(-110_i16));
assert_eq!(Step::backward_checked(30_020_i16, 50_050_usize), Some(-20_030_i16));
assert_eq!(Step::backward_checked(-10_i16, 40_000_usize), None);
assert_eq!(Step::backward_checked(-10_i16, 70_000_usize), None);
assert_eq!(Step::backward_checked(70_010_u128, 70_000_usize), Some(10_u128));
assert_eq!(Step::backward_checked(70_020_i128, 70_030_usize), Some(-10_i128));
assert_eq!(Step::backward_checked(10_u128, 7_usize), Some(3_u128));
assert_eq!(Step::backward_checked(10_u128, 11_usize), None);
assert_eq!(
Step::backward_checked(-0x7fff_ffff_ffff_ffff__ffff_ffff_ffff_ff00_i128, 0x100_usize),
Some(i128::MIN)
);
} }
#[test] #[test]

1
src/libcore/tests/lib.rs
View file

@ -22,6 +22,7 @@
#![feature(slice_partition_at_index)] #![feature(slice_partition_at_index)]
#![feature(specialization)] #![feature(specialization)]
#![feature(step_trait)] #![feature(step_trait)]
#![feature(step_trait_ext)]
#![feature(str_internals)] #![feature(str_internals)]
#![feature(test)] #![feature(test)]
#![feature(trusted_len)] #![feature(trusted_len)]

32
src/librustc_index/vec.rs
View file

@ -65,7 +65,7 @@ impl Idx for u32 {
/// `u32::MAX`. You can also customize things like the `Debug` impl, /// `u32::MAX`. You can also customize things like the `Debug` impl,
/// what traits are derived, and so forth via the macro. /// what traits are derived, and so forth via the macro.
#[macro_export] #[macro_export]
#[allow_internal_unstable(step_trait, rustc_attrs)] #[allow_internal_unstable(step_trait, step_trait_ext, rustc_attrs)]
macro_rules! newtype_index { macro_rules! newtype_index {
// ---- public rules ---- // ---- public rules ----
@ -181,7 +181,7 @@ macro_rules! newtype_index {
} }
} }
impl ::std::iter::Step for $type { unsafe impl ::std::iter::Step for $type {
#[inline] #[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> { fn steps_between(start: &Self, end: &Self) -> Option<usize> {
<usize as ::std::iter::Step>::steps_between( <usize as ::std::iter::Step>::steps_between(
@ -191,33 +191,13 @@ macro_rules! newtype_index {
} }
#[inline] #[inline]
fn replace_one(&mut self) -> Self { fn forward_checked(start: Self, u: usize) -> Option<Self> {
::std::mem::replace(self, Self::from_u32(1)) Self::index(start).checked_add(u).map(Self::from_usize)
} }
#[inline] #[inline]
fn replace_zero(&mut self) -> Self { fn backward_checked(start: Self, u: usize) -> Option<Self> {
::std::mem::replace(self, Self::from_u32(0)) Self::index(start).checked_sub(u).map(Self::from_usize)
}
#[inline]
fn add_one(&self) -> Self {
Self::from_usize(Self::index(*self) + 1)
}
#[inline]
fn sub_one(&self) -> Self {
Self::from_usize(Self::index(*self) - 1)
}
#[inline]
fn add_usize(&self, u: usize) -> Option<Self> {
Self::index(*self).checked_add(u).map(Self::from_usize)
}
#[inline]
fn sub_usize(&self, u: usize) -> Option<Self> {
Self::index(*self).checked_sub(u).map(Self::from_usize)
} }
} }

26
src/test/ui/impl-trait/example-calendar.rs
View file

@ -2,6 +2,7 @@
#![feature(fn_traits, #![feature(fn_traits,
step_trait, step_trait,
step_trait_ext,
unboxed_closures, unboxed_closures,
)] )]
@ -10,7 +11,6 @@
//! Originally converted to Rust by [Daniel Keep](https://github.com/DanielKeep). //! Originally converted to Rust by [Daniel Keep](https://github.com/DanielKeep).
use std::fmt::Write; use std::fmt::Write;
use std::mem;
/// Date representation. /// Date representation.
#[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)] #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
@ -156,32 +156,16 @@ impl<'a, 'b> std::ops::Add<&'b NaiveDate> for &'a NaiveDate {
} }
} }
impl std::iter::Step for NaiveDate { unsafe impl std::iter::Step for NaiveDate {
fn steps_between(_: &Self, _: &Self) -> Option<usize> { fn steps_between(_: &Self, _: &Self) -> Option<usize> {
unimplemented!() unimplemented!()
} }
fn replace_one(&mut self) -> Self { fn forward_checked(start: Self, n: usize) -> Option<Self> {
mem::replace(self, NaiveDate(0, 0, 1)) Some((0..n).fold(start, |x, _| x.succ()))
} }
fn replace_zero(&mut self) -> Self { fn backward_checked(_: Self, _: usize) -> Option<Self> {
mem::replace(self, NaiveDate(0, 0, 0))
}
fn add_one(&self) -> Self {
self.succ()
}
fn sub_one(&self) -> Self {
unimplemented!()
}
fn add_usize(&self, _: usize) -> Option<Self> {
unimplemented!()
}
fn sub_usize(&self, _: usize) -> Option<Self> {
unimplemented!() unimplemented!()
} }
} }