feat: Add optional context type getter (acts-project#3853)

Also adds a unit test.

Core/include/Acts/Utilities/detail/ContextType.hpp

@@ -79,6 +79,28 @@ class ContextType {
     return std::any_cast<const std::decay_t<T>&>(m_data);
   }
 
+  /// Retrieve a pointer to the contained type
+  ///
+  /// @note Returns `nullptr` if @p is not the contained type.
+  ///
+  /// @tparam T The type to attempt to retrieve the value as
+  /// @return Pointer to the contained value, may be null
+  template <typename T>
+  std::decay_t<T>* maybeGet() {
+    return std::any_cast<std::decay_t<T>>(&m_data);
+  }
+
+  /// Retrieve a pointer to the contained type
+  ///
+  /// @note Returns `nullptr` if @p is not the contained type.
+  ///
+  /// @tparam T The type to attempt to retrieve the value as
+  /// @return Pointer to the contained value, may be null
+  template <typename T>
+  const std::decay_t<T>* maybeGet() const {
+    return std::any_cast<const std::decay_t<T>>(&m_data);
+  }
+
   /// Check if the contained type is initialized.
   /// @return Boolean indicating whether a type is present
   bool hasValue() const { return m_data.has_value(); }

Tests/UnitTests/Core/Utilities/CMakeLists.txt

@@ -61,3 +61,4 @@ add_unittest(VectorHelpers VectorHelpersTests.cpp)
 
 add_unittest(TrackHelpers TrackHelpersTests.cpp)
 add_unittest(GraphViz GraphVizTests.cpp)
+add_unittest(ContextType ContextTypeTests.cpp)

Tests/UnitTests/Core/Utilities/ContextTypeTests.cpp

@@ -0,0 +1,38 @@
+// This file is part of the ACTS project.
+//
+// Copyright (C) 2016 CERN for the benefit of the ACTS project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#include <boost/test/tools/old/interface.hpp>
+#include <boost/test/unit_test.hpp>
+
+#include "Acts/Utilities/detail/ContextType.hpp"
+
+using namespace Acts;
+
+BOOST_AUTO_TEST_SUITE(ContextTypeTests)
+
+BOOST_AUTO_TEST_CASE(PackUnpack) {
+  ContextType ctx;
+
+  int v = 42;
+  ctx = v;
+
+  BOOST_CHECK_EQUAL(ctx.get<int>(), 42);
+  BOOST_CHECK_THROW(ctx.get<double>(), std::bad_any_cast);
+}
+
+BOOST_AUTO_TEST_CASE(MaybeUnpack) {
+  ContextType ctx;
+
+  int v = 42;
+  ctx = v;
+
+  BOOST_CHECK_EQUAL(*ctx.maybeGet<int>(), 42);
+  BOOST_CHECK_EQUAL(ctx.maybeGet<double>(), nullptr);
+}
+
+BOOST_AUTO_TEST_SUITE_END()