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//! The [`Instant`] struct and its associated `impl`s.
use core::borrow::Borrow;
use core::cmp::{Ord, Ordering, PartialEq, PartialOrd};
use core::ops::{Add, Sub};
use core::time::Duration as StdDuration;
use std::time::Instant as StdInstant;
use crate::Duration;
/// A measurement of a monotonically non-decreasing clock. Opaque and useful only with [`Duration`].
///
/// Instants are always guaranteed to be no less than any previously measured instant when created,
/// and are often useful for tasks such as measuring benchmarks or timing how long an operation
/// takes.
///
/// Note, however, that instants are not guaranteed to be **steady**. In other words, each tick of
/// the underlying clock may not be the same length (e.g. some seconds may be longer than others).
/// An instant may jump forwards or experience time dilation (slow down or speed up), but it will
/// never go backwards.
///
/// Instants are opaque types that can only be compared to one another. There is no method to get
/// "the number of seconds" from an instant. Instead, it only allows measuring the duration between
/// two instants (or comparing two instants).
///
/// This implementation allows for operations with signed [`Duration`]s, but is otherwise identical
/// to [`std::time::Instant`].
#[repr(transparent)]
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Instant(pub StdInstant);
impl Instant {
// region: delegation
/// Returns an `Instant` corresponding to "now".
///
/// ```rust
/// # use time::Instant;
/// println!("{:?}", Instant::now());
/// ```
pub fn now() -> Self {
Self(StdInstant::now())
}
/// Returns the amount of time elapsed since this instant was created. The duration will always
/// be nonnegative if the instant is not synthetically created.
///
/// ```rust
/// # use time::{Instant, ext::{NumericalStdDuration, NumericalDuration}};
/// # use std::thread;
/// let instant = Instant::now();
/// thread::sleep(1.std_milliseconds());
/// assert!(instant.elapsed() >= 1.milliseconds());
/// ```
pub fn elapsed(self) -> Duration {
Self::now() - self
}
// endregion delegation
// region: checked arithmetic
/// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be represented as
/// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
/// otherwise.
///
/// ```rust
/// # use time::{Instant, ext::NumericalDuration};
/// let now = Instant::now();
/// assert_eq!(now.checked_add(5.seconds()), Some(now + 5.seconds()));
/// assert_eq!(now.checked_add((-5).seconds()), Some(now + (-5).seconds()));
/// ```
pub fn checked_add(self, duration: Duration) -> Option<Self> {
if duration.is_zero() {
Some(self)
} else if duration.is_positive() {
self.0.checked_add(duration.unsigned_abs()).map(Self)
} else {
debug_assert!(duration.is_negative());
self.0.checked_sub(duration.unsigned_abs()).map(Self)
}
}
/// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be represented as
/// `Instant` (which means it's inside the bounds of the underlying data structure), `None`
/// otherwise.
///
/// ```rust
/// # use time::{Instant, ext::NumericalDuration};
/// let now = Instant::now();
/// assert_eq!(now.checked_sub(5.seconds()), Some(now - 5.seconds()));
/// assert_eq!(now.checked_sub((-5).seconds()), Some(now - (-5).seconds()));
/// ```
pub fn checked_sub(self, duration: Duration) -> Option<Self> {
if duration.is_zero() {
Some(self)
} else if duration.is_positive() {
self.0.checked_sub(duration.unsigned_abs()).map(Self)
} else {
debug_assert!(duration.is_negative());
self.0.checked_add(duration.unsigned_abs()).map(Self)
}
}
// endregion checked arithmetic
/// Obtain the inner [`std::time::Instant`].
///
/// ```rust
/// # use time::Instant;
/// let now = Instant::now();
/// assert_eq!(now.into_inner(), now.0);
/// ```
pub const fn into_inner(self) -> StdInstant {
self.0
}
}
// region: trait impls
impl From<StdInstant> for Instant {
fn from(instant: StdInstant) -> Self {
Self(instant)
}
}
impl From<Instant> for StdInstant {
fn from(instant: Instant) -> Self {
instant.0
}
}
impl Sub for Instant {
type Output = Duration;
fn sub(self, other: Self) -> Self::Output {
match self.0.cmp(&other.0) {
Ordering::Equal => Duration::ZERO,
Ordering::Greater => (self.0 - other.0)
.try_into()
.expect("overflow converting `std::time::Duration` to `time::Duration`"),
Ordering::Less => -Duration::try_from(other.0 - self.0)
.expect("overflow converting `std::time::Duration` to `time::Duration`"),
}
}
}
impl Sub<StdInstant> for Instant {
type Output = Duration;
fn sub(self, other: StdInstant) -> Self::Output {
self - Self(other)
}
}
impl Sub<Instant> for StdInstant {
type Output = Duration;
fn sub(self, other: Instant) -> Self::Output {
Instant(self) - other
}
}
impl Add<Duration> for Instant {
type Output = Self;
/// # Panics
///
/// This function may panic if the resulting point in time cannot be represented by the
/// underlying data structure.
fn add(self, duration: Duration) -> Self::Output {
if duration.is_positive() {
Self(self.0 + duration.unsigned_abs())
} else if duration.is_negative() {
#[allow(clippy::unchecked_duration_subtraction)]
Self(self.0 - duration.unsigned_abs())
} else {
debug_assert!(duration.is_zero());
self
}
}
}
impl Add<Duration> for StdInstant {
type Output = Self;
fn add(self, duration: Duration) -> Self::Output {
(Instant(self) + duration).0
}
}
impl Add<StdDuration> for Instant {
type Output = Self;
fn add(self, duration: StdDuration) -> Self::Output {
Self(self.0 + duration)
}
}
impl_add_assign!(Instant: Duration, StdDuration);
impl_add_assign!(StdInstant: Duration);
impl Sub<Duration> for Instant {
type Output = Self;
/// # Panics
///
/// This function may panic if the resulting point in time cannot be represented by the
/// underlying data structure.
fn sub(self, duration: Duration) -> Self::Output {
if duration.is_positive() {
#[allow(clippy::unchecked_duration_subtraction)]
Self(self.0 - duration.unsigned_abs())
} else if duration.is_negative() {
Self(self.0 + duration.unsigned_abs())
} else {
debug_assert!(duration.is_zero());
self
}
}
}
impl Sub<Duration> for StdInstant {
type Output = Self;
fn sub(self, duration: Duration) -> Self::Output {
(Instant(self) - duration).0
}
}
impl Sub<StdDuration> for Instant {
type Output = Self;
/// # Panics
///
/// This function may panic if the resulting point in time cannot be represented by the
/// underlying data structure.
fn sub(self, duration: StdDuration) -> Self::Output {
#[allow(clippy::unchecked_duration_subtraction)]
Self(self.0 - duration)
}
}
impl_sub_assign!(Instant: Duration, StdDuration);
impl_sub_assign!(StdInstant: Duration);
impl PartialEq<StdInstant> for Instant {
fn eq(&self, rhs: &StdInstant) -> bool {
self.0.eq(rhs)
}
}
impl PartialEq<Instant> for StdInstant {
fn eq(&self, rhs: &Instant) -> bool {
self.eq(&rhs.0)
}
}
impl PartialOrd<StdInstant> for Instant {
fn partial_cmp(&self, rhs: &StdInstant) -> Option<Ordering> {
self.0.partial_cmp(rhs)
}
}
impl PartialOrd<Instant> for StdInstant {
fn partial_cmp(&self, rhs: &Instant) -> Option<Ordering> {
self.partial_cmp(&rhs.0)
}
}
impl AsRef<StdInstant> for Instant {
fn as_ref(&self) -> &StdInstant {
&self.0
}
}
impl Borrow<StdInstant> for Instant {
fn borrow(&self) -> &StdInstant {
&self.0
}
}
// endregion trait impls