diff --git a/src/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs index b56a27c80bc83..403914c070780 100644 --- a/src/libstd/collections/hash/set.rs +++ b/src/libstd/collections/hash/set.rs @@ -618,6 +618,62 @@ impl HashSet self.map.get_key_value(value).map(|(k, _)| k) } + /// Inserts the given `value` into the set if it is not present, then + /// returns a reference to the value in the set. + /// + /// # Examples + /// + /// ``` + /// #![feature(hash_set_entry)] + /// + /// use std::collections::HashSet; + /// + /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect(); + /// assert_eq!(set.len(), 3); + /// assert_eq!(set.get_or_insert(2), &2); + /// assert_eq!(set.get_or_insert(100), &100); + /// assert_eq!(set.len(), 4); // 100 was inserted + /// ``` + #[inline] + #[unstable(feature = "hash_set_entry", issue = "60896")] + pub fn get_or_insert(&mut self, value: T) -> &T { + // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with + // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`. + self.map.raw_entry_mut().from_key(&value).or_insert(value, ()).0 + } + + /// Inserts a value computed from `f` into the set if the given `value` is + /// not present, then returns a reference to the value in the set. + /// + /// # Examples + /// + /// ``` + /// #![feature(hash_set_entry)] + /// + /// use std::collections::HashSet; + /// + /// let mut set: HashSet = ["cat", "dog", "horse"] + /// .iter().map(|&pet| pet.to_owned()).collect(); + /// + /// assert_eq!(set.len(), 3); + /// for &pet in &["cat", "dog", "fish"] { + /// let value = set.get_or_insert_with(pet, str::to_owned); + /// assert_eq!(value, pet); + /// } + /// assert_eq!(set.len(), 4); // a new "fish" was inserted + /// ``` + #[inline] + #[unstable(feature = "hash_set_entry", issue = "60896")] + pub fn get_or_insert_with(&mut self, value: &Q, f: F) -> &T + where T: Borrow, + Q: Hash + Eq, + F: FnOnce(&Q) -> T + { + // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with + // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`. + self.map.raw_entry_mut().from_key(value).or_insert_with(|| (f(value), ())).0 + } + /// Returns `true` if `self` has no elements in common with `other`. /// This is equivalent to checking for an empty intersection. ///