mirror of
https://github.com/wpilibsuite/allwpilib
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68 lines
2.3 KiB
C++
68 lines
2.3 KiB
C++
/*----------------------------------------------------------------------------*/
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/* Copyright (c) 2017-2018 FIRST. All Rights Reserved. */
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/* Open Source Software - may be modified and shared by FRC teams. The code */
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/* must be accompanied by the FIRST BSD license file in the root directory of */
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/* the project. */
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/*----------------------------------------------------------------------------*/
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#ifndef WPIUTIL_WPI_UIDVECTOR_H_
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#define WPIUTIL_WPI_UIDVECTOR_H_
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#include <utility>
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#include <vector>
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namespace wpi {
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// Vector which provides an integrated freelist for removal and reuse of
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// individual elements.
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// @tparam T element type; must be default-constructible and evaluate in
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// boolean context to false when "empty"
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// @tparam reuse_threshold how many free elements to store up before starting
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// to recycle them
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template <typename T, typename std::vector<T>::size_type reuse_threshold>
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class UidVector {
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public:
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typedef typename std::vector<T>::size_type size_type;
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bool empty() const { return m_active_count == 0; }
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size_type size() const { return m_vector.size(); }
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T& operator[](size_type i) { return m_vector[i]; }
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const T& operator[](size_type i) const { return m_vector[i]; }
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// Add a new T to the vector. If there are elements on the freelist,
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// reuses the last one; otherwise adds to the end of the vector.
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// Returns the resulting element index.
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template <class... Args>
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size_type emplace_back(Args&&... args) {
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size_type uid;
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if (m_free.size() < reuse_threshold) {
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uid = m_vector.size();
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m_vector.emplace_back(std::forward<Args>(args)...);
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} else {
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uid = m_free.front();
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m_free.erase(m_free.begin());
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m_vector[uid] = T(std::forward<Args>(args)...);
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}
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++m_active_count;
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return uid;
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}
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// Removes the identified element by replacing it with a default-constructed
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// one. The element is added to the freelist for later reuse.
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void erase(size_type uid) {
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if (uid >= m_vector.size() || !m_vector[uid]) return;
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m_free.push_back(uid);
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m_vector[uid] = T();
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--m_active_count;
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}
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private:
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std::vector<T> m_vector;
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std::vector<size_type> m_free;
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size_type m_active_count{0};
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};
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} // namespace wpi
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#endif // WPIUTIL_WPI_UIDVECTOR_H_
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