LibreOffice Module o3tl (master)  1

Update output object lazily This template collects data in input type, and updates the output type with the given update functor, but only if the output is requested. Useful if updating is expensive, or input changes frequently, but output is only comparatively seldom used.

LazyUpdate<InType,OutType,decltype(F)> myValue(F);
*myValue = newInput;
myValue->updateInput( this, that, those );
output( *myValue );


output( myValue.getOutValue() );

if the compiler does not recognize the const context.

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed
* with this work for additional information regarding copyright
* ownership. The ASF licenses this file to you under the Apache
* License, Version 2.0 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at .
#include <utility>
namespace o3tl
template<typename In, typename Out, typename Func> class LazyUpdate {
LazyUpdate(Func const & func): func_(func), input_(), dirty_(true) {}
In const & getInValue() const { return input_; }
Out const & getOutValue() const { return update(); }
In & operator *() {
dirty_ = true;
return input_;
dirty_ = true;
return &input_;
Out const & operator *() const { return update(); }
Out const * operator ->() const { return &update(); }
Out const & update() const {
if (dirty_) {
dirty_ = false;
return output_;
Func const func_;
mutable Out output_;
mutable bool dirty_;
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */