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* Copyright 2015 Canonical Ltd.
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation; version 3.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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#ifndef UBUNTUGESTURES_POOL_H
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#define UBUNTUGESTURES_POOL_H
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#include "ubuntugesturesglobal.h"
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Avoids unnecessary creations/initializations and deletions/destructions of items. Useful
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in a scenario where items are created and destroyed very frequently but the total number
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of items at any given time remains small. They're stored in a unordered fashion.
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To be used in Pool, ItemType needs to have the following methods:
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A constructor that takes no parameters. An object contructed with it must return false if
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- bool isValid() const;
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Returns wheter the object holds a valid , "filled" state or is empty.
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Used by Pool to check if the slot occupied by this object is actually available.
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Resets the object to its initial, empty, state. After calling this method, isValid() must
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template <class ItemType> class Pool
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Pool() : m_lastUsedIndex(-1) {
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Iterator() : index(-1), item(nullptr) {}
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Iterator(int index, ItemType *item)
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: index(index), item(item) {}
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ItemType *operator->() const { return item; }
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ItemType &operator*() const { return *item; }
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ItemType &value() const { return *item; }
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Iterator &operator= (const Iterator& other) {
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// by convention, always return *this
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operator bool() const { return item != nullptr; }
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ItemType &getEmptySlot() {
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Q_ASSERT(m_lastUsedIndex < m_slots.size());
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// Look for an in-between vacancy first
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for (int i = 0; i < m_lastUsedIndex; ++i) {
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ItemType &item = m_slots[i];
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if (!item.isValid()) {
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if (m_lastUsedIndex >= m_slots.size()) {
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m_slots.resize(m_lastUsedIndex + 1);
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return m_slots[m_lastUsedIndex];
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void freeSlot(Iterator &iterator) {
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m_slots[iterator.index].reset();
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if (iterator.index == m_lastUsedIndex) {
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} while (m_lastUsedIndex >= 0 && !m_slots.at(m_lastUsedIndex).isValid());
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// Iterates through all valid items (i.e. the occupied slots)
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// calling the given function, with the option of ending the loop early.
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// bool Func(Iterator& item)
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// Returning true means it wants to continue the "for" loop, false
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// terminates the loop.
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template<typename Func> void forEach(Func func) {
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for (it.index = 0; it.index <= m_lastUsedIndex; ++it.index) {
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it.item = &m_slots[it.index];
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if (!it.item->isValid())
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bool isEmpty() const { return m_lastUsedIndex == -1; }
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QVector<ItemType> m_slots;
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#endif // UBUNTUGESTURES_POOL_H