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Implement TrustedLen for ranges of all T: Step, make Step an unsafe t…
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…rait.
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@SimonSapin
SimonSapin committed Jul 24, 2017
1 parent 0a62269 commit 0ac7fca
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Showing 2 changed files with 31 additions and 44 deletions.
73 changes: 30 additions & 43 deletions src/libcore/iter/range.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,15 +17,23 @@ use super::{FusedIterator, TrustedLen};

/// Objects that have a notion of *successor* and *predecessor*
/// for the purpose of range iterators.
///
/// This trait is `unsafe` because implementations of the `unsafe` trait `TrustedLen`
/// depend on its implementations being correct.
#[unstable(feature = "step_trait",
reason = "recently redesigned",
issue = "42168")]
pub trait Step: Clone + PartialOrd + Sized {
pub unsafe trait Step: Clone + PartialOrd + Sized {
/// Returns the number of *successor* steps needed to get from `start` to `end`.
///
/// Returns `None` if that number would overflow `usize`
/// (or is infinite, if `end` would never be reached).
/// Returns `Some(0)` if `start` comes after (is greater than) or equals `end`.
///
/// This must hold for any `a`, `b`, and `n`:
///
/// * `steps_between(&a, &b) == Some(0)` if and only if `a >= b`.
/// * `steps_between(&a, &b) == Some(n)` if and only if `a.forward(n) == Some(b)`
/// * `steps_between(&a, &b) == Some(n)` if and only if `b.backward(n) == Some(a)`
fn steps_between(start: &Self, end: &Self) -> Option<usize>;

/// Returns the value that would be obtained by taking the *successor* of `self`,
Expand All @@ -35,6 +43,10 @@ pub trait Step: Clone + PartialOrd + Sized {
///
/// Note: `step_count == 1` is a common case,
/// used for example in `Iterator::next` for ranges.
///
/// This must hold for any `a`, `n`, and `m` where `n + m` doesn’t overflow:
///
/// * `a.forward(n).and_then(|x| x.forward(m)) == a.forward(n + m)`
fn forward(&self, step_count: usize) -> Option<Self>;

/// Returns the value that would be obtained by taking the *predecessor* of `self`,
Expand All @@ -44,6 +56,10 @@ pub trait Step: Clone + PartialOrd + Sized {
///
/// Note: `step_count == 1` is a common case,
/// used for example in `Iterator::next_back` for ranges.
///
/// This must hold for any `a`, `n`, and `m` where `n + m` doesn’t overflow:
///
/// * `a.backward(n).and_then(|x| x.backward(m)) == a.backward(n + m)`
fn backward(&self, step_count: usize) -> Option<Self>;
}

Expand All @@ -58,11 +74,9 @@ macro_rules! step_integer_impls {
#[unstable(feature = "step_trait",
reason = "recently redesigned",
issue = "42168")]
impl Step for $narrower_unsigned {
unsafe impl Step for $narrower_unsigned {
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
// NOTE: the safety of `unsafe impl TrustedLen` depends on
// this being correct!
if *start < *end {
// This relies on $narrower_unsigned <= usize
Some((*end - *start) as usize)
Expand Down Expand Up @@ -91,11 +105,9 @@ macro_rules! step_integer_impls {
#[unstable(feature = "step_trait",
reason = "recently redesigned",
issue = "42168")]
impl Step for $narrower_signed {
unsafe impl Step for $narrower_signed {
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
// NOTE: the safety of `unsafe impl TrustedLen` depends on
// this being correct!
if *start < *end {
// This relies on $narrower_signed <= usize
//
Expand Down Expand Up @@ -157,11 +169,9 @@ macro_rules! step_integer_impls {
#[unstable(feature = "step_trait",
reason = "recently redesigned",
issue = "42168")]
impl Step for $wider_unsigned {
unsafe impl Step for $wider_unsigned {
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
// NOTE: the safety of `unsafe impl TrustedLen` depends on
// this being correct!
if *start < *end {
usize::try_from(*end - *start).ok()
} else {
Expand All @@ -183,11 +193,9 @@ macro_rules! step_integer_impls {
#[unstable(feature = "step_trait",
reason = "recently redesigned",
issue = "42168")]
impl Step for $wider_signed {
unsafe impl Step for $wider_signed {
#[inline]
fn steps_between(start: &Self, end: &Self) -> Option<usize> {
// NOTE: the safety of `unsafe impl TrustedLen` depends on
// this being correct!
if *start < *end {
match end.checked_sub(*start) {
Some(diff) => usize::try_from(diff).ok(),
Expand Down Expand Up @@ -248,22 +256,6 @@ 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)*) => ($(
#[unstable(feature = "inclusive_range",
reason = "recently added, follows RFC",
issue = "28237")]
unsafe impl TrustedLen for ops::RangeInclusive<$t> { }
)*)
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step> Iterator for ops::Range<A> {
type Item = A;
Expand Down Expand Up @@ -335,19 +327,6 @@ range_incl_exact_iter_impl! {
i8
}

// These macros generate `TrustedLen` impls.
//
// They need to guarantee that .size_hint() is either exact, or that
// the upper bound is None when it does not fit the type limits.
range_trusted_len_impl! {
usize u8 u16 u32 u64 u128
isize i8 i16 i32 i64 i128
}
range_incl_trusted_len_impl! {
usize u8 u16 u32 u64 u128
isize i8 i16 i32 i64 i128
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Step> DoubleEndedIterator for ops::Range<A> {
#[inline]
Expand All @@ -362,6 +341,9 @@ impl<A: Step> DoubleEndedIterator for ops::Range<A> {
}
}

#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<T: Step> TrustedLen for ops::Range<T> {}

#[unstable(feature = "fused", issue = "35602")]
impl<A: Step> FusedIterator for ops::Range<A> {}

Expand Down Expand Up @@ -507,5 +489,10 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
}
}

#[unstable(feature = "inclusive_range",
reason = "recently added, follows RFC",
issue = "28237")]
unsafe impl<T: Step> TrustedLen for ops::RangeInclusive<T> { }

#[unstable(feature = "fused", issue = "35602")]
impl<A: Step> FusedIterator for ops::RangeInclusive<A> {}
2 changes: 1 addition & 1 deletion src/test/run-pass/impl-trait/example-calendar.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -161,7 +161,7 @@ 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> {
unimplemented!()
}
Expand Down

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