Reserve space in advance

2020-10-16 11:43:39 +02:00
parent 2ca0b85593
commit a7f2bb6343
4 changed files with 9 additions and 7 deletions
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -66,7 +66,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>

    let fmt = substr.nonself_args[0].clone();

-    let mut stmts = vec![];
+    let mut stmts = Vec::with_capacity(fields.len() + 2);
    match vdata {
        ast::VariantData::Tuple(..) | ast::VariantData::Unit(..) => {
            // tuple struct/"normal" variant