lazy_update.hxx

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#ifndef INCLUDED_O3TL_LAZY_UPDATE_HXX
#define INCLUDED_O3TL_LAZY_UPDATE_HXX
 
#include <utility>
 
namespace o3tl
{
    template<typename In, typename Out, typename Func> class LazyUpdate {
    public:
        LazyUpdate(Func func): func_(std::move(func)), input_(), dirty_(true) {}
 
        In const & getInValue() const { return input_; }
 
        Out const & getOutValue() const { return update(); }
 
        In & operator *() {
            dirty_ = true;
            return input_;
        }
 
        In * operator ->() {
            dirty_ = true;
            return &input_;
        }
 
        Out const & operator *() const { return update();  }
 
        Out const * operator ->() const { return &update(); }
 
    private:
        Out const & update() const {
            if (dirty_) {
                output_ = func_(input_);
                dirty_ = false;
            }
            return output_;
        }
 
        Func const func_;
        In input_;
        mutable Out output_;
        mutable bool dirty_;
    };
}
 
#endif
 
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