Write examples for {BTree,Hash}Set::{get,replace,take}

set.rs

@@ -527,6 +527,16 @@ impl<T, S> HashSet<T, S>
     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
     /// the value type.
     ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.get(&2), Some(&2));
+    /// assert_eq!(set.get(&4), None);
+    /// ```
+    ///
     /// [`Eq`]: ../../std/cmp/trait.Eq.html
     /// [`Hash`]: ../../std/hash/trait.Hash.html
     #[stable(feature = "set_recovery", since = "1.9.0")]
@@ -631,6 +641,19 @@ impl<T, S> HashSet<T, S>
 
     /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
     /// one. Returns the replaced value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut set = HashSet::new();
+    /// set.insert(Vec::<i32>::new());
+    ///
+    /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 0);
+    /// set.replace(Vec::with_capacity(10));
+    /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 10);
+    /// ```
     #[stable(feature = "set_recovery", since = "1.9.0")]
     pub fn replace(&mut self, value: T) -> Option<T> {
         Recover::replace(&mut self.map, value)
@@ -671,6 +694,16 @@ impl<T, S> HashSet<T, S>
     /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
     /// the value type.
     ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::collections::HashSet;
+    ///
+    /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.take(&2), Some(2));
+    /// assert_eq!(set.take(&2), None);
+    /// ```
+    ///
     /// [`Eq`]: ../../std/cmp/trait.Eq.html
     /// [`Hash`]: ../../std/hash/trait.Hash.html
     #[stable(feature = "set_recovery", since = "1.9.0")]