From 44e4a5b13a5c4ad7ee7522258ffe14467150c6a7 Mon Sep 17 00:00:00 2001
From: Chocobo1 <Chocobo1@users.noreply.github.com>
Date: Fri, 26 Apr 2019 01:48:40 +0800
Subject: [PATCH] Avoid performance penalty from type erasure

On average the affected code path is 0.1% faster and the result binary
is 10 KB smaller.
---
 src/base/settingvalue.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/base/settingvalue.h b/src/base/settingvalue.h
index 5ce8f3d8a..e3ff237c1 100644
--- a/src/base/settingvalue.h
+++ b/src/base/settingvalue.h
@@ -29,7 +29,6 @@
 #ifndef SETTINGVALUE_H
 #define SETTINGVALUE_H
 
-#include <functional>
 #include <type_traits>
 
 #include <QMetaEnum>
@@ -41,8 +40,6 @@
 template <typename T>
 class CachedSettingValue
 {
-    using ProxyFunc = std::function<T (const T&)>;
-
 public:
     explicit CachedSettingValue(const char *keyName, const T &defaultValue = T())
         : m_keyName(QLatin1String(keyName))
@@ -50,8 +47,11 @@ public:
     {
     }
 
+    // The signature of the ProxyFunc should be equivalent to the following:
+    // T proxyFunc(const T &a);
+    template <typename ProxyFunc>
     explicit CachedSettingValue(const char *keyName, const T &defaultValue
-            , const ProxyFunc &proxyFunc)
+                                , ProxyFunc proxyFunc)
         : m_keyName(QLatin1String(keyName))
         , m_value(proxyFunc(loadValue(defaultValue)))
     {