From 2e7df7eb8df4df4e7dd7c2bc641c64b78405ecf4 Mon Sep 17 00:00:00 2001
From: Phil Willoughby <philwill@fb.com>
Date: Mon, 26 Jun 2017 07:08:25 -0700
Subject: [PATCH] Improve efficiency of trivial toDelim calls

Summary:
`toDelim` with a single parameter of the same type as the target type was
previously copy-constructing its result. It will now construct it with perfect
forwarding which is more efficient if the input is a temporary.

This brings `toDelim` into line with the similar implementations of `to` and
`tryTo`

Reviewed By: yfeldblum

Differential Revision: D5301427

fbshipit-source-id: 843a2d93384de88cce42f26da6562a1a6ed0dc9c
---
 folly/Conv.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/folly/Conv.h b/folly/Conv.h
index 6cc32705..72518d80 100644
--- a/folly/Conv.h
+++ b/folly/Conv.h
@@ -986,11 +986,12 @@ to(Src value) {
  * toDelim<SomeString>(SomeString str) returns itself.
  */
 template <class Tgt, class Delim, class Src>
-typename std::enable_if<IsSomeString<Tgt>::value &&
-                            std::is_same<Tgt, Src>::value,
-                        Tgt>::type
-toDelim(const Delim& /* delim */, const Src& value) {
-  return value;
+typename std::enable_if<
+    IsSomeString<Tgt>::value &&
+        std::is_same<Tgt, typename std::decay<Src>::type>::value,
+    Tgt>::type
+toDelim(const Delim& /* delim */, Src&& value) {
+  return std::forward<Src>(value);
 }
 
 /**
-- 
2.34.1