refactor: Unify proxy iterator types

We have quite a few container types whose iterators are container-index
pairs. These currently have different implementations which can be
fairly easily unified under a single template.

Core/include/Acts/EventData/SpacePointContainer.hpp

@@ -12,9 +12,9 @@
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/SpacePointData.hpp"
 #include "Acts/EventData/SpacePointProxy.hpp"
-#include "Acts/EventData/SpacePointProxyIterator.hpp"
 #include "Acts/EventData/Utils.hpp"
 #include "Acts/Utilities/HashedString.hpp"
+#include "Acts/Utilities/Iterator.hpp"
 
 #include <any>
 #include <vector>
@@ -67,19 +67,22 @@ class SpacePointContainer {
  public:
   friend class Acts::SpacePointProxy<
       Acts::SpacePointContainer<container_t, holder_t>>;
-  friend class Acts::SpacePointProxyIterator<
-      Acts::SpacePointContainer<container_t, holder_t>>;
 
  public:
-  using iterator = Acts::SpacePointProxyIterator<
-      Acts::SpacePointContainer<container_t, holder_t>>;
-  using const_iterator = iterator;
-
   using SpacePointProxyType =
       Acts::SpacePointProxy<Acts::SpacePointContainer<container_t, holder_t>>;
+
+  using iterator =
+      ContainerIndexIterator<Acts::SpacePointContainer<container_t, holder_t>,
+                             SpacePointProxyType&, false>;
+  using const_iterator =
+      ContainerIndexIterator<Acts::SpacePointContainer<container_t, holder_t>,
+                             const SpacePointProxyType&, true>;
+
   using ValueType = typename container_t::ValueType;
   using ProxyType = SpacePointProxyType;
   using value_type = ProxyType;
+  using size_type = std::size_t;
 
  public:
   // Constructors
@@ -118,16 +121,23 @@ class SpacePointContainer {
 
   std::size_t size() const;
 
-  iterator begin() const;
-  iterator end() const;
+  iterator begin();
+  iterator end();
+  const_iterator cbegin() const;
+  const_iterator cend() const;
+  const_iterator begin() const;
+  const_iterator end() const;
 
+  ProxyType& at(const std::size_t n);
+  const ProxyType& at(const std::size_t n) const;
   const ValueType& sp(const std::size_t n) const;
 
  private:
   void initialize();
 
   const container_t& container() const;
   const ProxyType& proxy(const std::size_t n) const;
+  std::vector<ProxyType>& proxies();
   const std::vector<ProxyType>& proxies() const;
 
   float x(const std::size_t n) const;

Core/include/Acts/EventData/SpacePointContainer.ipp

@@ -104,23 +104,59 @@ std::size_t SpacePointContainer<container_t, holder_t>::size() const {
 }
 
 template <typename container_t, template <typename> class holder_t>
-typename SpacePointContainer<container_t, holder_t>::iterator
+typename SpacePointContainer<container_t, holder_t>::const_iterator
+SpacePointContainer<container_t, holder_t>::begin() {
+  return {*this, 0};
+}
+
+template <typename container_t, template <typename> class holder_t>
+typename SpacePointContainer<container_t, holder_t>::const_iterator
+SpacePointContainer<container_t, holder_t>::end() {
+  return {*this, size()};
+}
+
+template <typename container_t, template <typename> class holder_t>
+typename SpacePointContainer<container_t, holder_t>::const_iterator
 SpacePointContainer<container_t, holder_t>::begin() const {
   return {*this, 0};
 }
 
 template <typename container_t, template <typename> class holder_t>
-typename SpacePointContainer<container_t, holder_t>::iterator
+typename SpacePointContainer<container_t, holder_t>::const_iterator
 SpacePointContainer<container_t, holder_t>::end() const {
   return {*this, size()};
 }
 
+template <typename container_t, template <typename> class holder_t>
+typename SpacePointContainer<container_t, holder_t>::const_iterator
+SpacePointContainer<container_t, holder_t>::cbegin() const {
+  return {*this, 0};
+}
+
+template <typename container_t, template <typename> class holder_t>
+typename SpacePointContainer<container_t, holder_t>::const_iterator
+SpacePointContainer<container_t, holder_t>::cend() const {
+  return {*this, size()};
+}
+
 template <typename container_t, template <typename> class holder_t>
 const container_t& SpacePointContainer<container_t, holder_t>::container()
     const {
   return *m_container;
 }
 
+template <typename container_t, template <typename> class holder_t>
+typename SpacePointContainer<container_t, holder_t>::ProxyType&
+SpacePointContainer<container_t, holder_t>::at(const std::size_t n) {
+  return proxies().at(n);
+}
+
+template <typename container_t, template <typename> class holder_t>
+const typename SpacePointContainer<container_t, holder_t>::ProxyType&
+SpacePointContainer<container_t, holder_t>::at(const std::size_t n) const {
+  return proxies().at(n);
+}
+
 template <typename container_t, template <typename> class holder_t>
 const typename SpacePointContainer<container_t, holder_t>::ValueType&
 SpacePointContainer<container_t, holder_t>::sp(const std::size_t n) const {
@@ -173,6 +209,12 @@ SpacePointContainer<container_t, holder_t>::proxy(const std::size_t n) const {
   return proxies()[n];
 }
 
+template <typename container_t, template <typename> class holder_t>
+std::vector<typename SpacePointContainer<container_t, holder_t>::ProxyType>&
+SpacePointContainer<container_t, holder_t>::proxies() {
+  return m_proxies;
+}
+
 template <typename container_t, template <typename> class holder_t>
 const std::vector<
     typename SpacePointContainer<container_t, holder_t>::ProxyType>&

Core/include/Acts/EventData/TrackContainer.hpp

@@ -19,6 +19,8 @@
 #include "Acts/EventData/Utils.hpp"
 #include "Acts/Utilities/HashedString.hpp"
 #include "Acts/Utilities/Holders.hpp"
+#include "Acts/Utilities/Iterator.hpp"
+#include "Acts/Utilities/TypeTraits.hpp"
 #include "Acts/Utilities/UnitVectors.hpp"
 
 #include <any>
@@ -78,6 +80,12 @@ class TrackContainer {
   using ConstTrackStateProxy =
       typename MultiTrajectory<traj_t>::ConstTrackStateProxy;
 
+  using size_type = IndexType;
+  using iterator =
+      Acts::ContainerIndexIterator<TrackContainer, TrackProxy, false>;
+  using const_iterator =
+      Acts::ContainerIndexIterator<TrackContainer, ConstTrackProxy, true>;
+
 #ifndef DOXYGEN
   friend TrackProxy;
   friend ConstTrackProxy;
@@ -148,6 +156,21 @@ class TrackContainer {
     return {*this, itrack};
   }
 
+  /// Get a const track proxy for a track index
+  /// @param itrack the track index in the container
+  /// @return A const track proxy for the index
+  ConstTrackProxy at(IndexType itrack) const { return getTrack(itrack); }
+
+  /// Get a mutable track proxy for a track index
+  /// @note Only available if the track container is not read-only
+  /// @param itrack the track index in the container
+  /// @return A mutable track proxy for the index
+  TrackProxy at(IndexType itrack)
+    requires(!ReadOnly)
+  {
+    return {*this, itrack};
+  }
+
   /// Add a track to the container. Note this only creates the logical track and
   /// allocates memory. You can combine this with @c getTrack to obtain a track proxy
   /// @note Only available if the track container is not read-only
@@ -184,36 +207,28 @@ class TrackContainer {
   /// Get a mutable iterator to the first track in the container
   /// @note Only available if the track container is not read-only
   /// @return a mutable iterator to the first track
-  auto begin()
+  iterator begin()
     requires(!ReadOnly)
   {
-    return detail_tc::TrackProxyIterator<std::decay_t<decltype(*this)>,
-                                         TrackProxy, false>{*this, 0};
+    return iterator{*this, 0};
   }
 
   /// Get a past-the-end iterator for this container
   /// @note Only available if the track container is not read-only
   /// @return a past-the-end iterator
-  auto end()
+  iterator end()
     requires(!ReadOnly)
   {
-    return detail_tc::TrackProxyIterator<std::decay_t<decltype(*this)>,
-                                         TrackProxy, false>{*this, size()};
+    return iterator{*this, size()};
   }
 
   /// Get an const iterator to the first track in the container
   /// @return a const iterator to the first track
-  auto begin() const {
-    return detail_tc::TrackProxyIterator<std::decay_t<decltype(*this)>,
-                                         ConstTrackProxy, true>{*this, 0};
-  }
+  const_iterator begin() const { return const_iterator{*this, 0}; }
 
   /// Get a past-the-end iterator for this container
   /// @return a past-the-end iterator
-  auto end() const {
-    return detail_tc::TrackProxyIterator<std::decay_t<decltype(*this)>,
-                                         ConstTrackProxy, true>{*this, size()};
-  }
+  const_iterator end() const { return const_iterator{*this, size()}; }
 
   /// @}
 
@@ -411,8 +426,8 @@ class TrackContainer {
     }
   }
 
-  detail_tc::ConstIf<holder_t<track_container_t>, ReadOnly> m_container;
-  detail_tc::ConstIf<holder_t<traj_t>, ReadOnly> m_traj;
+  const_if_t<ReadOnly, holder_t<track_container_t>> m_container;
+  const_if_t<ReadOnly, holder_t<traj_t>> m_traj;
 };
 
 template <TrackContainerBackend track_container_t, typename traj_t>