Replace Vector::Empty with Vector::Inline using InlineArray.

CHANGELOG.md

@@ -30,6 +30,13 @@ The minimum supported Rust version is now 1.34.0.
 
 ### Fixed
 
+- `Vector` now uses
+  [`sized_chunks::InlineArray`](https://docs.rs/sized-chunks/0.3.0/sized_chunks/inline_array/struct.InlineArray.html)
+  instead of an `Empty` enum case to avoid allocation at very small sizes,
+  letting you store a handful of elements on the stack before needing to grow
+  into a full chunk. This has a beneficial effect on performance as well, as
+  there's no pointer into the heap to dereference, making it faster than
+  `std::vec::Vec` in this configuration.
 - Some complexity timings have been added and corrected. (#87)
 - `OrdSet::is_subset(&self, other)` now returns immediately when `self` is
   larger than `other` and thus could not possibly be a subset of it. (#87)

Cargo.toml

@@ -25,7 +25,7 @@ rustc_version = "0.2"
 
 [dependencies]
 typenum = "1.10"
-sized-chunks = "0.2.0"
+sized-chunks = "0.3.0"
 quickcheck = { version = "0.8", optional = true }
 proptest = { version = "0.9", optional = true }
 serde = { version = "1.0", optional = true }

rc/Cargo.toml

@@ -24,7 +24,7 @@ rustc_version = "0.2"
 
 [dependencies]
 typenum = "1.10"
-sized-chunks = "0.1.2"
+sized-chunks = "0.3.0"
 quickcheck = { version = "0.8", optional = true }
 proptest = { version = "0.9", optional = true }
 serde = { version = "1.0", optional = true }

src/vector/focus.rs

@@ -85,8 +85,6 @@ pub enum Focus<'a, A>
 where
     A: 'a,
 {
-    #[doc(hidden)]
-    Empty,
     #[doc(hidden)]
     Single(&'a [A]),
     #[doc(hidden)]
@@ -102,7 +100,7 @@ where
     /// [Vector]: enum.Vector.html
     pub fn new(vector: &'a Vector<A>) -> Self {
         match vector {
-            Vector::Empty => Focus::Empty,
+            Vector::Inline(chunk) => Focus::Single(chunk),
             Vector::Single(chunk) => Focus::Single(chunk),
             Vector::Full(tree) => Focus::Full(TreeFocus::new(tree)),
         }
@@ -113,7 +111,6 @@ where
     /// [Vector]: enum.Vector.html
     pub fn len(&self) -> usize {
         match self {
-            Focus::Empty => 0,
             Focus::Single(chunk) => chunk.len(),
             Focus::Full(tree) => tree.len(),
         }
@@ -129,7 +126,6 @@ where
     /// Get a reference to the value at a given index.
     pub fn get(&mut self, index: usize) -> Option<&A> {
         match self {
-            Focus::Empty => None,
             Focus::Single(chunk) => chunk.get(index),
             Focus::Full(tree) => tree.get(index),
         }
@@ -152,7 +148,6 @@ where
             panic!("vector::Focus::chunk_at: index out of bounds");
         }
         match self {
-            Focus::Empty => (0..0, &[]),
             Focus::Single(chunk) => (0..len, chunk),
             Focus::Full(tree) => tree.get_chunk(index),
         }
@@ -190,7 +185,6 @@ where
             panic!("vector::Focus::narrow: range out of bounds");
         }
         match self {
-            Focus::Empty => Focus::Empty,
             Focus::Single(chunk) => Focus::Single(&chunk[r]),
             Focus::Full(tree) => Focus::Full(tree.narrow(r)),
         }
@@ -231,7 +225,6 @@ where
             panic!("vector::Focus::split_at: index out of bounds");
         }
         match self {
-            Focus::Empty => (Focus::Empty, Focus::Empty),
             Focus::Single(chunk) => {
                 let (left, right) = chunk.split_at(index);
                 (Focus::Single(left), Focus::Single(right))
@@ -262,7 +255,6 @@ where
 {
     fn clone(&self) -> Self {
         match self {
-            Focus::Empty => Focus::Empty,
             Focus::Single(chunk) => Focus::Single(chunk),
             Focus::Full(tree) => Focus::Full(tree.clone()),
         }
@@ -483,8 +475,6 @@ pub enum FocusMut<'a, A>
 where
     A: 'a,
 {
-    #[doc(hidden)]
-    Empty,
     #[doc(hidden)]
     Single(&'a mut [A]),
     #[doc(hidden)]
@@ -498,7 +488,7 @@ where
     /// Construct a `FocusMut` for a `Vector`.
     pub fn new(vector: &'a mut Vector<A>) -> Self {
         match vector {
-            Vector::Empty => FocusMut::Empty,
+            Vector::Inline(chunk) => FocusMut::Single(chunk),
             Vector::Single(chunk) => FocusMut::Single(Ref::make_mut(chunk).as_mut_slice()),
             Vector::Full(tree) => FocusMut::Full(TreeFocusMut::new(tree)),
         }
@@ -507,7 +497,6 @@ where
     /// Get the length of the focused `Vector`.
     pub fn len(&self) -> usize {
         match self {
-            FocusMut::Empty => 0,
             FocusMut::Single(chunk) => chunk.len(),
             FocusMut::Full(tree) => tree.len(),
         }
@@ -526,7 +515,6 @@ where
     /// Get a mutable reference to the value at a given index.
     pub fn get_mut(&mut self, index: usize) -> Option<&mut A> {
         match self {
-            FocusMut::Empty => None,
             FocusMut::Single(chunk) => chunk.get_mut(index),
             FocusMut::Full(tree) => tree.get(index),
         }
@@ -645,7 +633,6 @@ where
             panic!("vector::FocusMut::chunk_at: index out of bounds");
         }
         match self {
-            FocusMut::Empty => (0..0, &mut []),
             FocusMut::Single(chunk) => (0..len, chunk),
             FocusMut::Full(tree) => {
                 let (range, chunk) = tree.get_chunk(index);
@@ -686,7 +673,6 @@ where
             panic!("vector::FocusMut::narrow: range out of bounds");
         }
         match self {
-            FocusMut::Empty => FocusMut::Empty,
             FocusMut::Single(chunk) => FocusMut::Single(&mut chunk[r]),
             FocusMut::Full(tree) => FocusMut::Full(tree.narrow(r)),
         }
@@ -734,7 +720,6 @@ where
             panic!("vector::FocusMut::split_at: index out of bounds");
         }
         match self {
-            FocusMut::Empty => (FocusMut::Empty, FocusMut::Empty),
             FocusMut::Single(chunk) => {
                 let (left, right) = chunk.split_at_mut(index);
                 (FocusMut::Single(left), FocusMut::Single(right))
@@ -749,7 +734,6 @@ where
     /// Convert a `FocusMut` into a `Focus`.
     pub fn unmut(self) -> Focus<'a, A> {
         match self {
-            FocusMut::Empty => Focus::Empty,
             FocusMut::Single(chunk) => Focus::Single(chunk),
             FocusMut::Full(mut tree) => Focus::Full(TreeFocus {
                 tree: {