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       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             : #ifndef INCLUDED_O3TL_LAZY_UPDATE_HXX
      21             : #define INCLUDED_O3TL_LAZY_UPDATE_HXX
      22             : 
      23             : #include <sal/config.h>
      24             : 
      25             : #include <utility>
      26             : 
      27             : namespace o3tl
      28             : {
      29             :     /** Update output object lazily
      30             : 
      31             :         This template collects data in input type, and updates the
      32             :         output type with the given update functor, but only if the
      33             :         output is requested. Useful if updating is expensive, or input
      34             :         changes frequently, but output is only comparatively seldom
      35             :         used.
      36             : 
      37             :         @example
      38             :         <pre>
      39             : LazyUpdate<InType,OutType,decltype(F)> myValue(F);
      40             : *myValue = newInput;
      41             : myValue->updateInput( this, that, those );
      42             : 
      43             : output( *myValue );
      44             :         </pre>
      45             :         or
      46             :         <pre>
      47             : output( myValue.getOutValue() );
      48             :         </pre>
      49             :         if the compiler does not recognize the const context.
      50             :      */
      51           0 :     template<typename In, typename Out, typename Func> class LazyUpdate {
      52             :     public:
      53           0 :         LazyUpdate(Func const & func): func_(func), input_(), dirty_(true) {}
      54             : 
      55             :         template<typename T> void setInValue(T && in) {
      56             :             dirty_ = true;
      57             :             input_ = std::forward(in);
      58             :         }
      59             : 
      60           0 :         In const & getInValue() const { return input_; }
      61             : 
      62           0 :         Out const & getOutValue() const { return update(); }
      63             : 
      64           0 :         In & operator *() {
      65           0 :             dirty_ = true;
      66           0 :             return input_;
      67             :         }
      68             : 
      69           0 :         In * operator ->() {
      70           0 :             dirty_ = true;
      71           0 :             return &input_;
      72             :         }
      73             : 
      74           0 :         Out const & operator *() const { return update();  }
      75             : 
      76             :         Out const * operator ->() const { return &update(); }
      77             : 
      78             :     private:
      79           0 :         Out const & update() const {
      80           0 :             if (dirty_) {
      81           0 :                 output_ = func_(input_);
      82           0 :                 dirty_ = false;
      83             :             }
      84           0 :             return output_;
      85             :         }
      86             : 
      87             :         Func const func_;
      88             :         In input_;
      89             :         mutable Out output_;
      90             :         mutable bool dirty_;
      91             :     };
      92             : }
      93             : 
      94             : #endif
      95             : 
      96             : /* vim:set shiftwidth=4 softtabstop=4 expandtab: */