QScopeGuard: Make constructor public

With Class Template Argument Deduction users might want to use the constructor
itself instead of a separate helper function. In both cases it's possible to let
the compiler deduce the template arguments.

Try to make the usefulness of the helper function in the absence of CTAD still
clear in the documentation.

Change-Id: I9b07983c1fb276a6dd9e7ed4c3e606764e9b68ca
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>

1 files changed, 25 insertions, 12 deletions

diff --git a/src/corelib/tools/qscopeguard.h b/src/corelib/tools/qscopeguard.h
index 40d2747b1d..4d2e715df1 100644
--- a/src/corelib/tools/qscopeguard.h
+++ b/src/corelib/tools/qscopeguard.h
@@ -1,6 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2018 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Sérgio Martins <sergio.martins@kdab.com>
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -45,10 +46,6 @@
 
 QT_BEGIN_NAMESPACE
 
-
-template <typename F> class QScopeGuard;
-template <typename F> QScopeGuard<F> qScopeGuard(F f);
-
 template <typename F>
 class
 #if __has_cpp_attribute(nodiscard)
@@ -59,13 +56,23 @@ Q_REQUIRED_RESULT
 QScopeGuard
 {
 public:
+    explicit QScopeGuard(F &&f) noexcept
+        : m_func(std::move(f))
+    {
+    }
+
+    explicit QScopeGuard(const F &f) noexcept
+        : m_func(f)
+    {
+    }
+
     QScopeGuard(QScopeGuard &&other) noexcept
         : m_func(std::move(other.m_func))
         , m_invoke(qExchange(other.m_invoke, false))
     {
     }
 
-    ~QScopeGuard()
+    ~QScopeGuard() noexcept
     {
         if (m_invoke)
             m_func();
@@ -77,28 +84,34 @@ public:
     }
 
 private:
-    explicit QScopeGuard(F &&f) noexcept
-        : m_func(std::move(f))
-    {
-    }
-
     Q_DISABLE_COPY(QScopeGuard)
 
     F m_func;
     bool m_invoke = true;
-    friend QScopeGuard qScopeGuard<F>(F);
 };
 
+#ifdef __cpp_deduction_guides
+template <typename F> QScopeGuard(F(&)()) -> QScopeGuard<F(*)()>;
+#endif
 
 template <typename F>
 #if __has_cpp_attribute(nodiscard)
 Q_REQUIRED_RESULT
 #endif
-QScopeGuard<F> qScopeGuard(F f)
+QScopeGuard<F> qScopeGuard(F &&f)
 {
     return QScopeGuard<F>(std::move(f));
 }
 
+template <typename F>
+#if __has_cpp_attribute(nodiscard)
+Q_REQUIRED_RESULT
+#endif
+QScopeGuard<F> qScopeGuard(const F &f)
+{
+    return QScopeGuard<F>(f);
+}
+
 QT_END_NAMESPACE
 
 #endif // QSCOPEGUARD_H