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PdfForQtLib/sources/pdfutils.h

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+//    Copyright (C) 2019 Jakub Melka
+//
+//    This file is part of PdfForQt.
+//
+//    PdfForQt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    PdfForQt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.
+
+
+#ifndef PDFUTILS_H
+#define PDFUTILS_H
+
+namespace pdf
+{
+
+/// Class for easy storing of cached item. This class is not thread safe,
+/// and for this reason, access function are not constant (they can modify the
+/// object).
+template<typename T>
+class PDFCachedItem
+{
+public:
+    explicit inline PDFCachedItem() :
+        m_dirty(true),
+        m_object()
+    {
+
+    }
+
+    /// Returns the cached object. If object is dirty, then cached object is refreshed.
+    /// \param holder Holder object, which owns the cached item
+    /// \param function Refresh function
+    template<typename H>
+    inline const T& get(const H* holder, T(H::* function)(void) const)
+    {
+        if (m_dirty)
+        {
+            m_object = (holder->*function)();
+            m_dirty = false;
+        }
+
+        return m_object;
+    }
+
+    /// Invalidates the cached item, so it must be refreshed from the cache next time,
+    /// if it is accessed.
+    inline void dirty()
+    {
+        m_dirty = true;
+        m_object = T();
+    }
+
+private:
+    bool m_dirty;
+    T m_object;
+};
+
+}   // namespace pdf
+
+#endif // PDFUTILS_H