include/unotools/weakref.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  *
   9  * This file incorporates work covered by the following license notice:
  10  *
  11  *   Licensed to the Apache Software Foundation (ASF) under one or more
  12  *   contributor license agreements. See the NOTICE file distributed
  13  *   with this work for additional information regarding copyright
  14  *   ownership. The ASF licenses this file to you under the Apache
  15  *   License, Version 2.0 (the "License"); you may not use this file
  16  *   except in compliance with the License. You may obtain a copy of
  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 /*
  21  * This file is part of LibreOffice published API.
  22  */
  23 #pragma once
  24
  25 #include <sal/config.h>
  26
  27 #include <com/sun/star/uno/Reference.hxx>
  28 #include <com/sun/star/uno/XInterface.hpp>
  29 #include <cppuhelper/weakref.hxx>
  30 #include <cppuhelper/weak.hxx>
  31 #include <rtl/ref.hxx>
  32 #include <type_traits>
  33
  34 namespace unotools
  35 {
  36 /** The WeakReference<> holds a weak reference to an object.
  37
  38     That object must implement the css::uno::XWeak interface.
  39
  40     The WeakReference itself is *not* thread safe, just as
  41     Reference itself isn't, but the implementation of the listeners etc.
  42     behind it *is* thread-safe, so multiple threads can have their own
  43     WeakReferences to the same XWeak object.
  44
  45     @tparam interface_type Must be a C++ implementation class type, not a UNO interface type.  (See
  46     the C++20 requires-clause on the get member.  That clause is not put on the class as a whole to
  47     avoid overly tight requirements on when interface_type needs to be complete.)
  48 */
  49 template <class interface_type>
  50 class SAL_WARN_UNUSED WeakReference : public com::sun::star::uno::WeakReferenceHelper
  51 {
  52 public:
  53     /** Default ctor.  Creates an empty weak reference.
  54     */
  55     WeakReference()
  56         : WeakReferenceHelper()
  57     {
  58     }
  59
  60     /** Copy ctor.  Initialize this reference with a hard reference.
  61
  62         @param rRef another hard ref
  63     */
  64     WeakReference(const rtl::Reference<interface_type>& rRef)
  65         : WeakReferenceHelper(css::uno::Reference<css::uno::XWeak>(rRef))
  66     {
  67     }
  68
  69     /** Copy ctor.  Initialize this reference with a hard reference.
  70
  71         @param rRef another hard ref
  72     */
  73     WeakReference(interface_type& rRef)
  74         : WeakReferenceHelper(&rRef)
  75     {
  76     }
  77
  78     /** Copy ctor.  Initialize this reference with a hard reference.
  79
  80         @param rRef another hard ref
  81     */
  82     WeakReference(interface_type* pRef)
  83         : WeakReferenceHelper(
  84               css::uno::Reference<css::uno::XWeak>(static_cast<cppu::OWeakObject*>(pRef)))
  85     {
  86     }
  87
  88     /** Releases this reference and takes over hard reference xInt.
  89         If the implementation behind xInt does not support XWeak
  90         or XInt is null, then this reference is null.
  91
  92         @param xInt another hard reference
  93     */
  94     WeakReference& operator=(const rtl::Reference<interface_type>& xInt)
  95     {
  96         WeakReferenceHelper::operator=(xInt);
  97         return *this;
  98     }
  99
 100     WeakReference& operator=(rtl::Reference<interface_type>&& xInt)
 101     {
 102         WeakReferenceHelper::operator=(std::move(xInt));
 103         return *this;
 104     }
 105
 106     WeakReference& operator=(interface_type* pInt)
 107     {
 108         WeakReferenceHelper::operator=(
 109             css::uno::Reference<css::uno::XWeak>(static_cast<::cppu::OWeakObject*>(pInt)));
 110         return *this;
 111     }
 112
 113     /**  Gets a hard reference to the object.
 114
 115          @return hard reference or null, if the weakly referenced interface has gone
 116     */
 117     rtl::Reference<interface_type> SAL_CALL get() const
 118 #if __cplusplus >= 202002L
 119         requires(!cppu::detail::isUnoInterfaceType<interface_type>)
 120 #endif
 121     {
 122         css::uno::Reference<css::uno::XInterface> xInterface = WeakReferenceHelper::get();
 123         // If XInterface is an ambiguous base of interface_type, we have to use dynamic_cast,
 124         // otherwise we can use the faster static_cast.
 125         if constexpr (std::is_convertible_v<interface_type*, css::uno::XInterface*>)
 126             return static_cast<interface_type*>(xInterface.get());
 127         else
 128             return dynamic_cast<interface_type*>(xInterface.get());
 129     }
 130
 131     /**  Gets a hard reference to the object.
 132
 133          @return hard reference or null, if the weakly referenced interface has gone
 134     */
 135     operator ::rtl::Reference<interface_type>() const { return get(); }
 136 };
 137 }
 138
 139 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */