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Optimize Option::clone to Copy when possible #76551

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Optimize Option::clone to Copy when possible #76551

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46176eb
Optimize Option::clone to Copy when possible
ridiculousfish Sep 9, 2020
bebfcfd
Optimize Option<Range>::clone
ridiculousfish Sep 10, 2020
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32 changes: 28 additions & 4 deletions library/core/src/option.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -134,8 +134,8 @@
use crate::iter::{FromIterator, FusedIterator, TrustedLen};
use crate::pin::Pin;
use crate::{
convert, fmt, hint, mem,
ops::{self, Deref, DerefMut},
convert, fmt, hint, mem, ptr,
ops::{self, Deref, DerefMut, Range},
};

/// The `Option` type. See [the module level documentation](self) for more.
Expand Down Expand Up @@ -1228,22 +1228,46 @@ fn expect_none_failed(msg: &str, value: &dyn fmt::Debug) -> ! {
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone> Clone for Option<T> {
#[inline]
fn clone(&self) -> Self {
default fn clone(&self) -> Self {
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Make sure you check how specialization is used for iterators. As I understand it, it's always behind a helper trait so that specialization doesn't leak out into the public API (like I think this would).

match self {
Some(x) => Some(x.clone()),
None => None,
}
}

#[inline]
fn clone_from(&mut self, source: &Self) {
default fn clone_from(&mut self, source: &Self) {
match (self, source) {
(Some(to), Some(from)) => to.clone_from(from),
(to, from) => *to = from.clone(),
}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Copy> Clone for Option<T> {
#[inline]
fn clone(&self) -> Self {
*self
}

#[inline]
fn clone_from(&mut self, source: &Self) {
*self = *source
}
}

// Range<T> is not Copy even if T is copy (see #27186),
// so provide an efficient implementation.
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Copy> Clone for Option<Range<T>> {
#[inline]
fn clone(&self) -> Self {
// SAFETY: 'self' is not Drop so memcpy is OK.
unsafe { ptr::read(self as *const Self) }
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Default for Option<T> {
/// Returns [`None`][Option::None].
Expand Down