Add UidVector (used in both ntcore and cscore Notifier). (#22)

src/main/native/include/support/UidVector.h

@@ -0,0 +1,59 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2017. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_SUPPORT_UIDVECTOR_H_
+#define WPIUTIL_SUPPORT_UIDVECTOR_H_
+
+#include <vector>
+
+namespace wpi {
+
+// Vector which provides an integrated freelist for removal and reuse of
+// individual elements.
+template <typename T>
+class UidVector {
+ public:
+  typedef typename std::vector<T>::size_type size_type;
+
+  size_type size() const { return m_vector.size(); }
+  T& operator[](size_type i) { return m_vector[i]; }
+  const T& operator[](size_type i) const { return m_vector[i]; }
+
+  // Add a new T to the vector.  If there are elements on the freelist,
+  // reuses the last one; otherwise adds to the end of the vector.
+  // Returns the resulting element index (+1).
+  template <class... Args>
+  unsigned int emplace_back(Args&&... args) {
+    unsigned int uid;
+    if (m_free.empty()) {
+      uid = m_vector.size();
+      m_vector.emplace_back(std::forward<Args>(args)...);
+    } else {
+      uid = m_free.back();
+      m_free.pop_back();
+      m_vector[uid] = T(std::forward<Args>(args)...);
+    }
+    return uid + 1;
+  }
+
+  // Removes the identified element by replacing it with a default-constructed
+  // one.  The element is added to the freelist for later reuse.
+  void erase(unsigned int uid) {
+    --uid;
+    if (uid >= m_vector.size() || !m_vector[uid]) return;
+    m_free.push_back(uid);
+    m_vector[uid] = T();
+  }
+
+ private:
+  std::vector<T> m_vector;
+  std::vector<unsigned int> m_free;
+};
+
+}  // namespace wpi
+
+#endif  // WPIUTIL_SUPPORT_UIDVECTOR_H_