From c60ed5d22c4c2a4885fdfdfa8c6b008d79b0fc29 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Thu, 1 Nov 2018 05:35:20 +1100 Subject: [PATCH] Share empty `Vec`s more within `MatcherPos::matches`. `create_matches` creates a `Vec>>`. Even though all the inner `Vec`s are empty, each one is created separately. This commit changes `create_matches` so it instead creates one empty inner `Vec`, and shares it. The commit also changes `MatcherPos::matches` to a boxed slice, because its length doesn't change. --- src/libsyntax/ext/tt/macro_parser.rs | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/src/libsyntax/ext/tt/macro_parser.rs b/src/libsyntax/ext/tt/macro_parser.rs index 03a8376e763..bf91a233f7c 100644 --- a/src/libsyntax/ext/tt/macro_parser.rs +++ b/src/libsyntax/ext/tt/macro_parser.rs @@ -168,7 +168,7 @@ struct MatcherPos<'a> { /// all bound matches from the submatcher into the shared top-level `matches` vector. If `sep` /// and `up` are `Some`, then `matches` is _not_ the shared top-level list. Instead, if one /// wants the shared `matches`, one should use `up.matches`. - matches: Vec>>, + matches: Box<[Rc>]>, /// The position in `matches` corresponding to the first metavar in this matcher's sequence of /// token trees. In other words, the first metavar in the first token of `top_elts` corresponds /// to `matches[match_lo]`. @@ -278,9 +278,14 @@ pub fn count_names(ms: &[TokenTree]) -> usize { }) } -/// Initialize `len` empty shared `Vec`s to be used to store matches of metavars. -fn create_matches(len: usize) -> Vec>> { - (0..len).into_iter().map(|_| Rc::new(Vec::new())).collect() +/// `len` `Vec`s (initially shared and empty) that will store matches of metavars. +fn create_matches(len: usize) -> Box<[Rc>]> { + if len == 0 { + vec![] + } else { + let empty_matches = Rc::new(Vec::new()); + vec![empty_matches.clone(); len] + }.into_boxed_slice() } /// Generate the top-level matcher position in which the "dot" is before the first token of the