From a566a3acc84386e4738711d27a250f63e59cbb6b Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 18 Oct 2019 08:37:27 +0200
Subject: Optimize config::required() to move default value if possible

---
 libbuild2/config/utility.hxx | 11 +++++++----
 libbuild2/config/utility.txx |  4 ++--
 2 files changed, 9 insertions(+), 6 deletions(-)

(limited to 'libbuild2')

diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index b1995b6..cfb7177 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -43,7 +43,7 @@ namespace build2
     pair<lookup, bool>
     required (scope& root,
               const variable&,
-              const T& default_value,
+              T&& default_value,
               bool override = false,
               uint64_t save_flags = 0);
 
@@ -53,12 +53,15 @@ namespace build2
     inline pair<lookup, bool>
     required (scope& root,
               const string& name,
-              const T& default_value,
+              T&& default_value,
               bool override = false,
               uint64_t save_flags = 0)
     {
-      return required (
-        root, root.ctx.var_pool[name], default_value, override, save_flags);
+      return required (root,
+                       root.ctx.var_pool[name],
+                       std::forward<T> (default_value), // VC14
+                       override,
+                       save_flags);
     }
 
     inline pair<lookup, bool>
diff --git a/libbuild2/config/utility.txx b/libbuild2/config/utility.txx
index 9c1455f..4c4e305 100644
--- a/libbuild2/config/utility.txx
+++ b/libbuild2/config/utility.txx
@@ -13,7 +13,7 @@ namespace build2
     pair<lookup, bool>
     required (scope& root,
               const variable& var,
-              const T& def_val,
+              T&& def_val,
               bool def_ovr,
               uint64_t save_flags)
     {
@@ -35,7 +35,7 @@ namespace build2
       //
       if (!l.defined () || (def_ovr && !l.belongs (root)))
       {
-        value& v (root.assign (var) = def_val);
+        value& v (root.assign (var) = std::forward<T> (def_val)); // VC14
         v.extra = true; // Default value flag.
 
         n = (save_flags & save_commented) == 0; // Absence means default.
-- 
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