Implemented some helper functions

Partially implemented some of the easier functions from here
servo/rust-smallvec#220 (comment)

Cargo.toml

@@ -8,4 +8,4 @@ documentation = "https://cfallin.github.io/rust-smallset/smallset/"
 license = "MIT"
 
 [dependencies]
-smallvec = "0.1"
+smallvec = "1.4.1"

src/lib.rs

@@ -4,13 +4,17 @@
 // Copyright (c) 2016 Chris Fallin <[email protected]>. Released under the MIT license.
 //
 
+extern crate smallvec;
+
+use std::borrow::Borrow;
 use std::fmt;
+use std::hash::Hash;
 use std::iter::{FromIterator, IntoIterator};
 use std::slice::Iter;
 
-extern crate smallvec;
 use smallvec::{Array, SmallVec};
 
+
 /// A `SmallSet` is an unordered set of elements. It is designed to work best
 /// for very small sets (no more than ten or so elements). In order to support
 /// small sets very efficiently, it stores elements in a simple unordered array.
@@ -37,15 +41,15 @@ use smallvec::{Array, SmallVec};
 /// assert!(s.contains(&1));
 /// ```
 pub struct SmallSet<A: Array>
-where
-    A::Item: PartialEq + Eq,
+    where
+        A::Item: PartialEq + Eq,
 {
     elements: SmallVec<A>,
 }
 
 impl<A: Array> SmallSet<A>
-where
-    A::Item: PartialEq + Eq,
+    where
+        A::Item: PartialEq + Eq,
 {
     /// Creates a new, empty `SmallSet`.
     pub fn new() -> SmallSet<A> {
@@ -98,11 +102,48 @@ where
     pub fn clear(&mut self) {
         self.elements.clear();
     }
+
+    //
+    pub fn get(&self, value: &A::Item) -> Option<&A::Item> {
+        self.elements.iter().find(|x| (value).eq(&x))
+    }
+
+    pub fn take(&mut self, value: &A::Item) -> Option<A::Item> {
+        if let Some(pos) = self.elements.iter().position(|e| *e == *value) {
+            let result = self.elements.remove(pos);
+            Some(result)
+        } else {
+            None
+        }
+    }
+
+    // Adds a value to the set, replacing the existing value, if any, that is equal to the given one. Returns the replaced value.
+    pub fn replace(&mut self, value: A::Item) -> Option<A::Item> {
+        if let Some(pos) = self.elements.iter().position(|e| *e == value) {
+            let result = self.elements.remove(pos);
+            self.elements.insert(pos, value);
+            Some(result)
+        } else {
+            None
+        }
+    }
+
+    pub fn drain<R>(&mut self, range: R) -> smallvec::Drain<A>
+        where
+            R: core::ops::RangeBounds<usize>,
+    {
+        self.elements.drain(range)
+    }
+
+    pub fn retain<F>(&mut self, f: F)
+        where F: FnMut(&mut A::Item) -> bool {
+        self.elements.retain(f)
+    }
 }
 
 impl<A: Array> Clone for SmallSet<A>
-where
-    A::Item: PartialEq + Eq + Clone,
+    where
+        A::Item: PartialEq + Eq + Clone,
 {
     fn clone(&self) -> SmallSet<A> {
         SmallSet {
@@ -112,21 +153,21 @@ where
 }
 
 impl<A: Array> fmt::Debug for SmallSet<A>
-where
-    A::Item: PartialEq + Eq + fmt::Debug,
+    where
+        A::Item: PartialEq + Eq + fmt::Debug,
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         self.elements.fmt(f)
     }
 }
 
 impl<A: Array> FromIterator<A::Item> for SmallSet<A>
-where
-    A::Item: PartialEq + Eq,
+    where
+        A::Item: PartialEq + Eq,
 {
     fn from_iter<T>(iter: T) -> Self
-    where
-        T: IntoIterator<Item = A::Item>,
+        where
+            T: IntoIterator<Item=A::Item>,
     {
         SmallSet {
             elements: SmallVec::from_iter(iter),
@@ -136,9 +177,10 @@ where
 
 #[cfg(test)]
 mod test {
-    use super::*;
     use std::fmt::Write;
 
+    use super::*;
+
     #[test]
     fn test_basic_set() {
         let mut s: SmallSet<[u32; 2]> = SmallSet::new();