Make `TokenStream` use `Option`.
Because that's the more typical way of representing an all-or-nothing
type.
diff --git a/src/libsyntax/tokenstream.rs b/src/libsyntax/tokenstream.rs
index d5c3624..f5d2d6f 100644
--- a/src/libsyntax/tokenstream.rs
+++ b/src/libsyntax/tokenstream.rs
@@ -141,11 +141,13 @@
/// The goal is for procedural macros to work with `TokenStream`s and `TokenTree`s
/// instead of a representation of the abstract syntax tree.
/// Today's `TokenTree`s can still contain AST via `Token::Interpolated` for back-compat.
+///
+/// The use of `Option` is an optimization that avoids the need for an
+/// allocation when the stream is empty. However, it is not guaranteed that an
+/// empty stream is represented with `None`; it may be represented as a `Some`
+/// around an empty `Vec`.
#[derive(Clone, Debug)]
-pub enum TokenStream {
- Empty,
- Stream(Lrc<Vec<TreeAndJoint>>),
-}
+pub struct TokenStream(Option<Lrc<Vec<TreeAndJoint>>>);
pub type TreeAndJoint = (TokenTree, IsJoint);
@@ -166,7 +168,7 @@
/// separating the two arguments with a comma for diagnostic suggestions.
pub(crate) fn add_comma(&self) -> Option<(TokenStream, Span)> {
// Used to suggest if a user writes `foo!(a b);`
- if let TokenStream::Stream(ref stream) = self {
+ if let Some(ref stream) = self.0 {
let mut suggestion = None;
let mut iter = stream.iter().enumerate().peekable();
while let Some((pos, ts)) = iter.next() {
@@ -230,7 +232,7 @@
impl TokenStream {
pub fn len(&self) -> usize {
- if let TokenStream::Stream(ref slice) = self {
+ if let Some(ref slice) = self.0 {
slice.len()
} else {
0
@@ -238,13 +240,13 @@
}
pub fn empty() -> TokenStream {
- TokenStream::Empty
+ TokenStream(None)
}
pub fn is_empty(&self) -> bool {
- match self {
- TokenStream::Empty => true,
- _ => false,
+ match self.0 {
+ None => true,
+ Some(ref stream) => stream.is_empty(),
}
}
@@ -255,9 +257,9 @@
_ => {
let mut vec = vec![];
for stream in streams {
- match stream {
- TokenStream::Empty => {},
- TokenStream::Stream(stream2) => vec.extend(stream2.iter().cloned()),
+ match stream.0 {
+ None => {},
+ Some(stream2) => vec.extend(stream2.iter().cloned()),
}
}
TokenStream::new(vec)
@@ -267,15 +269,14 @@
pub fn new(streams: Vec<TreeAndJoint>) -> TokenStream {
match streams.len() {
- 0 => TokenStream::empty(),
- _ => TokenStream::Stream(Lrc::new(streams)),
+ 0 => TokenStream(None),
+ _ => TokenStream(Some(Lrc::new(streams))),
}
}
pub fn append_to_tree_and_joint_vec(self, vec: &mut Vec<TreeAndJoint>) {
- match self {
- TokenStream::Empty => {}
- TokenStream::Stream(stream) => vec.extend(stream.iter().cloned()),
+ if let Some(stream) = self.0 {
+ vec.extend(stream.iter().cloned());
}
}
@@ -340,41 +341,36 @@
}
pub fn map_enumerated<F: FnMut(usize, TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
- match self {
- TokenStream::Empty => TokenStream::Empty,
- TokenStream::Stream(stream) => TokenStream::Stream(Lrc::new(
+ TokenStream(self.0.map(|stream| {
+ Lrc::new(
stream
.iter()
.enumerate()
.map(|(i, (tree, is_joint))| (f(i, tree.clone()), *is_joint))
- .collect()
- )),
- }
+ .collect())
+ }))
}
pub fn map<F: FnMut(TokenTree) -> TokenTree>(self, mut f: F) -> TokenStream {
- match self {
- TokenStream::Empty => TokenStream::Empty,
- TokenStream::Stream(stream) => TokenStream::Stream(Lrc::new(
+ TokenStream(self.0.map(|stream| {
+ Lrc::new(
stream
.iter()
.map(|(tree, is_joint)| (f(tree.clone()), *is_joint))
- .collect()
- )),
- }
+ .collect())
+ }))
}
- fn first_tree_and_joint(&self) -> Option<(TokenTree, IsJoint)> {
- match self {
- TokenStream::Empty => None,
- TokenStream::Stream(ref stream) => Some(stream.first().unwrap().clone())
- }
+ fn first_tree_and_joint(&self) -> Option<TreeAndJoint> {
+ self.0.as_ref().map(|stream| {
+ stream.first().unwrap().clone()
+ })
}
fn last_tree_if_joint(&self) -> Option<TokenTree> {
- match self {
- TokenStream::Empty => None,
- TokenStream::Stream(ref stream) => {
+ match self.0 {
+ None => None,
+ Some(ref stream) => {
if let (tree, Joint) = stream.last().unwrap() {
Some(tree.clone())
} else {
@@ -418,21 +414,21 @@
}
fn push_all_but_last_tree(&mut self, stream: &TokenStream) {
- if let TokenStream::Stream(ref streams) = stream {
+ if let Some(ref streams) = stream.0 {
let len = streams.len();
match len {
1 => {}
- _ => self.0.push(TokenStream::Stream(Lrc::new(streams[0 .. len - 1].to_vec()))),
+ _ => self.0.push(TokenStream(Some(Lrc::new(streams[0 .. len - 1].to_vec())))),
}
}
}
fn push_all_but_first_tree(&mut self, stream: &TokenStream) {
- if let TokenStream::Stream(ref streams) = stream {
+ if let Some(ref streams) = stream.0 {
let len = streams.len();
match len {
1 => {}
- _ => self.0.push(TokenStream::Stream(Lrc::new(streams[1 .. len].to_vec()))),
+ _ => self.0.push(TokenStream(Some(Lrc::new(streams[1 .. len].to_vec())))),
}
}
}
@@ -458,9 +454,9 @@
}
pub fn next_with_joint(&mut self) -> Option<TreeAndJoint> {
- match self.stream {
- TokenStream::Empty => None,
- TokenStream::Stream(ref stream) => {
+ match self.stream.0 {
+ None => None,
+ Some(ref stream) => {
if self.index < stream.len() {
self.index += 1;
Some(stream[self.index - 1].clone())
@@ -476,16 +472,15 @@
return;
}
let index = self.index;
- let stream = mem::replace(&mut self.stream, TokenStream::Empty);
+ let stream = mem::replace(&mut self.stream, TokenStream(None));
*self = TokenStream::from_streams(vec![stream, new_stream]).into_trees();
self.index = index;
}
pub fn look_ahead(&self, n: usize) -> Option<TokenTree> {
- match self.stream {
- TokenStream::Empty => None,
- TokenStream::Stream(ref stream) =>
- stream[self.index ..].get(n).map(|(tree, _)| tree.clone()),
+ match self.stream.0 {
+ None => None,
+ Some(ref stream) => stream[self.index ..].get(n).map(|(tree, _)| tree.clone()),
}
}
}
