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Make TokenStream use Option.
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Because that's the more typical way of representing an all-or-nothing
type.
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@nnethercote
nnethercote committed Jan 14, 2019
1 parent ba31d83 commit 7285724
Showing 1 changed file with 45 additions and 50 deletions.
95 changes: 45 additions & 50 deletions src/libsyntax/tokenstream.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -141,11 +141,13 @@ impl TokenTree {
/// 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);

Expand All @@ -166,7 +168,7 @@ impl TokenStream {
/// 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() {
Expand Down Expand Up @@ -230,21 +232,21 @@ impl PartialEq<TokenStream> for TokenStream {

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
}
}

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(),
}
}

Expand All @@ -255,9 +257,9 @@ impl TokenStream {
_ => {
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)
Expand All @@ -267,15 +269,14 @@ impl TokenStream {

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());
}
}

Expand Down Expand Up @@ -340,41 +341,36 @@ impl TokenStream {
}

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 {
Expand Down Expand Up @@ -418,21 +414,21 @@ impl TokenStreamBuilder {
}

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())))),
}
}
}
Expand All @@ -458,9 +454,9 @@ impl Cursor {
}

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())
Expand All @@ -476,16 +472,15 @@ impl Cursor {
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()),
}
}
}
Expand Down

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