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btree: cleanup difference, intersection, is_subset #147808

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Nov 7, 2025
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btree: cleanup difference, intersection, is_subset #147808

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179 changes: 86 additions & 93 deletions library/alloc/src/collections/btree/set.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -427,39 +427,35 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
where
T: Ord,
{
let (self_min, self_max) =
if let (Some(self_min), Some(self_max)) = (self.first(), self.last()) {
(self_min, self_max)
} else {
return Difference { inner: DifferenceInner::Iterate(self.iter()) };
};
let (other_min, other_max) =
if let (Some(other_min), Some(other_max)) = (other.first(), other.last()) {
(other_min, other_max)
} else {
return Difference { inner: DifferenceInner::Iterate(self.iter()) };
};
Difference {
inner: match (self_min.cmp(other_max), self_max.cmp(other_min)) {
(Greater, _) | (_, Less) => DifferenceInner::Iterate(self.iter()),
(Equal, _) => {
let mut self_iter = self.iter();
self_iter.next();
DifferenceInner::Iterate(self_iter)
}
(_, Equal) => {
let mut self_iter = self.iter();
self_iter.next_back();
DifferenceInner::Iterate(self_iter)
}
_ if self.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
DifferenceInner::Search { self_iter: self.iter(), other_set: other }
}
_ => DifferenceInner::Stitch {
self_iter: self.iter(),
other_iter: other.iter().peekable(),
if let Some(self_min) = self.first()
&& let Some(self_max) = self.last()
&& let Some(other_min) = other.first()
&& let Some(other_max) = other.last()
{
Difference {
inner: match (self_min.cmp(other_max), self_max.cmp(other_min)) {
(Greater, _) | (_, Less) => DifferenceInner::Iterate(self.iter()),
(Equal, _) => {
let mut self_iter = self.iter();
self_iter.next();
DifferenceInner::Iterate(self_iter)
}
(_, Equal) => {
let mut self_iter = self.iter();
self_iter.next_back();
DifferenceInner::Iterate(self_iter)
}
_ if self.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
DifferenceInner::Search { self_iter: self.iter(), other_set: other }
}
_ => DifferenceInner::Stitch {
self_iter: self.iter(),
other_iter: other.iter().peekable(),
},
},
},
}
} else {
Difference { inner: DifferenceInner::Iterate(self.iter()) }
}
}

Expand Down Expand Up @@ -519,31 +515,27 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
where
T: Ord,
{
let (self_min, self_max) =
if let (Some(self_min), Some(self_max)) = (self.first(), self.last()) {
(self_min, self_max)
} else {
return Intersection { inner: IntersectionInner::Answer(None) };
};
let (other_min, other_max) =
if let (Some(other_min), Some(other_max)) = (other.first(), other.last()) {
(other_min, other_max)
} else {
return Intersection { inner: IntersectionInner::Answer(None) };
};
Intersection {
inner: match (self_min.cmp(other_max), self_max.cmp(other_min)) {
(Greater, _) | (_, Less) => IntersectionInner::Answer(None),
(Equal, _) => IntersectionInner::Answer(Some(self_min)),
(_, Equal) => IntersectionInner::Answer(Some(self_max)),
_ if self.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
IntersectionInner::Search { small_iter: self.iter(), large_set: other }
}
_ if other.len() <= self.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
IntersectionInner::Search { small_iter: other.iter(), large_set: self }
}
_ => IntersectionInner::Stitch { a: self.iter(), b: other.iter() },
},
if let Some(self_min) = self.first()
&& let Some(self_max) = self.last()
&& let Some(other_min) = other.first()
&& let Some(other_max) = other.last()
{
Intersection {
inner: match (self_min.cmp(other_max), self_max.cmp(other_min)) {
(Greater, _) | (_, Less) => IntersectionInner::Answer(None),
(Equal, _) => IntersectionInner::Answer(Some(self_min)),
(_, Equal) => IntersectionInner::Answer(Some(self_max)),
_ if self.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
IntersectionInner::Search { small_iter: self.iter(), large_set: other }
}
_ if other.len() <= self.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF => {
IntersectionInner::Search { small_iter: other.iter(), large_set: self }
}
_ => IntersectionInner::Stitch { a: self.iter(), b: other.iter() },
},
}
} else {
Intersection { inner: IntersectionInner::Answer(None) }
}
}

Expand Down Expand Up @@ -694,55 +686,56 @@ impl<T, A: Allocator + Clone> BTreeSet<T, A> {
// Same result as self.difference(other).next().is_none()
// but the code below is faster (hugely in some cases).
if self.len() > other.len() {
return false;
return false; // self has more elements than other
}
let (self_min, self_max) =
if let (Some(self_min), Some(self_max)) = (self.first(), self.last()) {
(self_min, self_max)
} else {
return true; // self is empty
};
let (other_min, other_max) =
if let (Some(other_min), Some(other_max)) = (other.first(), other.last()) {
(other_min, other_max)
} else {
return false; // other is empty
};
let (Some(self_min), Some(self_max)) = (self.first(), self.last()) else {
return true; // self is empty
};
let (Some(other_min), Some(other_max)) = (other.first(), other.last()) else {
return false; // other is empty
};
let mut self_iter = self.iter();
match self_min.cmp(other_min) {
Less => return false,
Less => return false, // other does not contain self_min
Equal => {
self_iter.next();
self_iter.next(); // self_min is contained in other, so remove it from consideration
// other_min is now not in self_iter (used below)
}
Greater => (),
}
Greater => {} // other_min is not in self_iter (used below)
};

match self_max.cmp(other_max) {
Greater => return false,
Greater => return false, // other does not contain self_max
Equal => {
self_iter.next_back();
self_iter.next_back(); // self_max is contained in other, so remove it from consideration
// other_max is now not in self_iter (used below)
}
Less => (),
}
Less => {} // other_max is not in self_iter (used below)
};
if self_iter.len() <= other.len() / ITER_PERFORMANCE_TIPPING_SIZE_DIFF {
for next in self_iter {
if !other.contains(next) {
return false;
}
}
self_iter.all(|e| other.contains(e))
} else {
let mut other_iter = other.iter();
other_iter.next();
other_iter.next_back();
let mut self_next = self_iter.next();
while let Some(self1) = self_next {
match other_iter.next().map_or(Less, |other1| self1.cmp(other1)) {
Less => return false,
Equal => self_next = self_iter.next(),
Greater => (),
}
{
// remove other_min and other_max as they are not in self_iter (see above)
other_iter.next();
other_iter.next_back();
}
// custom `self_iter.all(|e| other.contains(e))`
self_iter.all(|self1| {
while let Some(other1) = other_iter.next() {
match other1.cmp(self1) {
// happens up to `ITER_PERFORMANCE_TIPPING_SIZE_DIFF * self.len() - 1` times
Less => continue, // skip over elements that are smaller
// happens `self.len()` times
Equal => return true, // self1 is in other
// happens only once
Greater => return false, // self1 is not in other
}
}
false
})
}
true
}

/// Returns `true` if the set is a superset of another,
Expand Down
2 changes: 1 addition & 1 deletion library/alloctests/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ repository = "https://github.com/rust-lang/rust.git"
description = "Tests for the Rust Allocation Library"
autotests = false
autobenches = false
edition = "2021"
edition = "2024"

[lib]
path = "lib.rs"
Expand Down
2 changes: 1 addition & 1 deletion tests/run-make/alloc-no-oom-handling/rmake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use run_make_support::{rustc, source_root};

fn main() {
rustc()
.edition("2021")
.edition("2024")
.arg("-Dwarnings")
.crate_type("rlib")
.input(source_root().join("library/alloc/src/lib.rs"))
Expand Down
2 changes: 1 addition & 1 deletion tests/run-make/alloc-no-rc/rmake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use run_make_support::{rustc, source_root};

fn main() {
rustc()
.edition("2021")
.edition("2024")
.arg("-Dwarnings")
.crate_type("rlib")
.input(source_root().join("library/alloc/src/lib.rs"))
Expand Down
2 changes: 1 addition & 1 deletion tests/run-make/alloc-no-sync/rmake.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use run_make_support::{rustc, source_root};

fn main() {
rustc()
.edition("2021")
.edition("2024")
.arg("-Dwarnings")
.crate_type("rlib")
.input(source_root().join("library/alloc/src/lib.rs"))
Expand Down
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