itertools breaking changes

0.15.0

61 breaking changes, first published June 16, 2026.

• Removed itertools::Position::First
  itertools::Position::First was removed in itertools 0.15.0 crates.io
• Removed itertools::Position::Last
  itertools::Position::Last was removed in itertools 0.15.0 crates.io
• Removed itertools::Position::Middle
  itertools::Position::Middle was removed in itertools 0.15.0 crates.io
• Removed itertools::Position::Only
  itertools::Position::Only was removed in itertools 0.15.0 crates.io
• Behavior changed collect_vec
  Calling collect_vec and discarding its result now produces a compiler warning, which may fail builds that deny warnings. github.com
• Signature changed itertools::CombinationsWithReplacement
  Was struct CombinationsWithReplacement<I> where I: Iterator, I::Item: Clone,; now type CombinationsWithReplacement<I> = CombinationsWithReplacementGeneric<I, Box<[usize]>>. crates.io
• Signature changed itertools::Duplicates
  Was type Duplicates<I> = private::DuplicatesBy<I, <I as Iterator>::Item, private::ById>; now type Duplicates<I, S = RandomState> = private::DuplicatesBy<I, <I as Iterator>::Item, private::ById, S>. crates.io
• Signature changed itertools::DuplicatesBy
  Was type DuplicatesBy<I, V, F> = private::DuplicatesBy<I, V, private::ByFn<F>>; now type DuplicatesBy<I, V, F, S = RandomState> = private::DuplicatesBy<I, V, private::ByFn<F>, S>. crates.io
• Signature changed itertools::GroupingMap
  Was struct GroupingMap<I>; now struct GroupingMap<I, S = RandomState> where S: BuildHasher,. crates.io
• Signature changed itertools::GroupingMap::aggregate
  Was fn aggregate<FO, R>(self, mut operation: FO) -> HashMap<K, R> where FO: FnMut(Option<R>, &K, V) -> Option<R>,; now fn aggregate<FO, R>(self, mut operation: FO) -> HashMap<K, R, S> where FO: FnMut(Option<R>, &K, V) -> Option<R>,. crates.io

And 51 more in this version.

Check your code

These are the changes. To see which of them reach your code, scan a public repository, or have your coding agent call check_code with your manifest or lockfile over MCP. The API reads every change in every version, not only the newest. On Team and up, a fix pull request opens for the changes that reach a connected repository. Nothing merges or deploys.