avoid string copies in attrNames sort comparison

symbols can also be cast to string_view, which compares the same but doesn't
require a copy of both symbol names on every comparison.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 7b0e6e7df..365595c92 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -2163,7 +2163,10 @@ static void prim_attrValues(EvalState & state, const Pos & pos, Value * * args,
         v.listElems()[n++] = (Value *) &i;
 
     std::sort(v.listElems(), v.listElems() + n,
-        [](Value * v1, Value * v2) { return (string) ((Attr *) v1)->name < (string) ((Attr *) v2)->name; });
+        [](Value * v1, Value * v2) {
+            std::string_view s1 = ((Attr *) v1)->name, s2 = ((Attr *) v2)->name;
+            return s1 < s2;
+        });
 
     for (unsigned int i = 0; i < n; ++i)
         v.listElems()[i] = ((Attr *) v.listElems()[i])->value;