From ad3db57a52986ebafc06ee37a2e23ce21e463fb6 Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Sun, 14 Jul 2024 22:02:13 -0700
Subject: [PATCH] Use Option's discriminant as its size hint
---
core/src/option.rs | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/core/src/option.rs b/core/src/option.rs
index 8ec7716012f59..1a8fe1e6051ad 100644
--- a/core/src/option.rs
+++ b/core/src/option.rs
@@ -770,6 +770,13 @@ impl<T> Option<T> {
}
}
+ #[inline]
+ const fn len(&self) -> usize {
+ // Using the intrinsic avoids emitting a branch to get the 0 or 1.
+ let discriminant: isize = crate::intrinsics::discriminant_value(self);
+ discriminant as usize
+ }
+
/// Returns a slice of the contained value, if any. If this is `None`, an
/// empty slice is returned. This can be useful to have a single type of
/// iterator over an `Option` or slice.
@@ -812,7 +819,7 @@ impl<T> Option<T> {
unsafe {
slice::from_raw_parts(
(self as *const Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
- self.is_some() as usize,
+ self.len(),
)
}
}
@@ -869,7 +876,7 @@ impl<T> Option<T> {
unsafe {
slice::from_raw_parts_mut(
(self as *mut Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
- self.is_some() as usize,
+ self.len(),
)
}
}
@@ -2242,10 +2249,8 @@ impl<A> Iterator for Item<A> {
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
- match self.opt {
- Some(_) => (1, Some(1)),
- None => (0, Some(0)),
- }
+ let len = self.len();
+ (len, Some(len))
}
}
@@ -2256,7 +2261,12 @@ impl<A> DoubleEndedIterator for Item<A> {
}
}
-impl<A> ExactSizeIterator for Item<A> {}
+impl<A> ExactSizeIterator for Item<A> {
+ #[inline]
+ fn len(&self) -> usize {
+ self.opt.len()
+ }
+}
impl<A> FusedIterator for Item<A> {}
unsafe impl<A> TrustedLen for Item<A> {}