Rollup merge of #47162 - stjepang:cleanup-btreeset, r=alexcrichton

Remove `T: Ord` bound from `BTreeSet::{is_empty, len}`

This change makes the API for `BTreeSet` more consistent with `BTreeMap`, where `BTreeMap::{is_empty, len}` don't require `T: Ord` either.

Also, it reduces the number of `impl`s for `BTreeSet`, making the generated documentation look much cleaner. Closes #47138.

cc @rust-lang/libs

src/liballoc/btree/set.rs

@@ -228,43 +228,7 @@ impl<T: Ord> BTreeSet<T> {
     pub fn new() -> BTreeSet<T> {
         BTreeSet { map: BTreeMap::new() }
     }
-}
-
-impl<T> BTreeSet<T> {
-    /// Gets an iterator that visits the values in the `BTreeSet` in ascending order.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::collections::BTreeSet;
-    ///
-    /// let set: BTreeSet<usize> = [1, 2, 3].iter().cloned().collect();
-    /// let mut set_iter = set.iter();
-    /// assert_eq!(set_iter.next(), Some(&1));
-    /// assert_eq!(set_iter.next(), Some(&2));
-    /// assert_eq!(set_iter.next(), Some(&3));
-    /// assert_eq!(set_iter.next(), None);
-    /// ```
-    ///
-    /// Values returned by the iterator are returned in ascending order:
-    ///
-    /// ```
-    /// use std::collections::BTreeSet;
-    ///
-    /// let set: BTreeSet<usize> = [3, 1, 2].iter().cloned().collect();
-    /// let mut set_iter = set.iter();
-    /// assert_eq!(set_iter.next(), Some(&1));
-    /// assert_eq!(set_iter.next(), Some(&2));
-    /// assert_eq!(set_iter.next(), Some(&3));
-    /// assert_eq!(set_iter.next(), None);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn iter(&self) -> Iter<T> {
-        Iter { iter: self.map.keys() }
-    }
-}
 
-impl<T: Ord> BTreeSet<T> {
     /// Constructs a double-ended iterator over a sub-range of elements in the set.
     /// The simplest way is to use the range syntax `min..max`, thus `range(min..max)` will
     /// yield elements from min (inclusive) to max (exclusive).
@@ -293,9 +257,7 @@ pub fn range<K: ?Sized, R>(&self, range: R) -> Range<T>
     {
         Range { iter: self.map.range(range) }
     }
-}
 
-impl<T: Ord> BTreeSet<T> {
     /// Visits the values representing the difference,
     /// i.e. the values that are in `self` but not in `other`,
     /// in ascending order.
@@ -408,40 +370,6 @@ pub fn union<'a>(&'a self, other: &'a BTreeSet<T>) -> Union<'a, T> {
         }
     }
 
-    /// Returns the number of elements in the set.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::collections::BTreeSet;
-    ///
-    /// let mut v = BTreeSet::new();
-    /// assert_eq!(v.len(), 0);
-    /// v.insert(1);
-    /// assert_eq!(v.len(), 1);
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn len(&self) -> usize {
-        self.map.len()
-    }
-
-    /// Returns `true` if the set contains no elements.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::collections::BTreeSet;
-    ///
-    /// let mut v = BTreeSet::new();
-    /// assert!(v.is_empty());
-    /// v.insert(1);
-    /// assert!(!v.is_empty());
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn is_empty(&self) -> bool {
-        self.len() == 0
-    }
-
     /// Clears the set, removing all values.
     ///
     /// # Examples
@@ -724,6 +652,74 @@ pub fn split_off<Q: ?Sized + Ord>(&mut self, key: &Q) -> Self where T: Borrow<Q>
     }
 }
 
+impl<T> BTreeSet<T> {
+    /// Gets an iterator that visits the values in the `BTreeSet` in ascending order.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::BTreeSet;
+    ///
+    /// let set: BTreeSet<usize> = [1, 2, 3].iter().cloned().collect();
+    /// let mut set_iter = set.iter();
+    /// assert_eq!(set_iter.next(), Some(&1));
+    /// assert_eq!(set_iter.next(), Some(&2));
+    /// assert_eq!(set_iter.next(), Some(&3));
+    /// assert_eq!(set_iter.next(), None);
+    /// ```
+    ///
+    /// Values returned by the iterator are returned in ascending order:
+    ///
+    /// ```
+    /// use std::collections::BTreeSet;
+    ///
+    /// let set: BTreeSet<usize> = [3, 1, 2].iter().cloned().collect();
+    /// let mut set_iter = set.iter();
+    /// assert_eq!(set_iter.next(), Some(&1));
+    /// assert_eq!(set_iter.next(), Some(&2));
+    /// assert_eq!(set_iter.next(), Some(&3));
+    /// assert_eq!(set_iter.next(), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter(&self) -> Iter<T> {
+        Iter { iter: self.map.keys() }
+    }
+
+    /// Returns the number of elements in the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::BTreeSet;
+    ///
+    /// let mut v = BTreeSet::new();
+    /// assert_eq!(v.len(), 0);
+    /// v.insert(1);
+    /// assert_eq!(v.len(), 1);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    /// Returns `true` if the set contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::BTreeSet;
+    ///
+    /// let mut v = BTreeSet::new();
+    /// assert!(v.is_empty());
+    /// v.insert(1);
+    /// assert!(!v.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord> FromIterator<T> for BTreeSet<T> {
     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BTreeSet<T> {