feat: Delegate construction with tag type

Core/include/Acts/Utilities/Delegate.hpp

@@ -20,6 +20,11 @@ namespace Acts {
 /// Ownership enum for @c Delegate
 enum class DelegateType { Owning, NonOwning };
 
+template <auto C>
+struct DelegateFuncTag {
+  explicit constexpr DelegateFuncTag() = default;
+};
+
 // Specialization needed for defaulting ownership and for R(Args...) syntax
 template <typename, typename H = void, DelegateType = DelegateType::NonOwning>
 class Delegate;
@@ -91,6 +96,26 @@ class Delegate<R(Args...), H, O> {
     connect(callable);
   }
 
+  /// Constructor with a compile-time free function pointer
+  /// @tparam Callable The compile-time free function pointer
+  /// @note @c DelegateFuncTag is used to communicate the callable type
+  template <auto Callable>
+  Delegate(DelegateFuncTag<Callable>) {
+    connect<Callable>();
+  }
+
+  /// Constructor with a compile-time member function pointer and instance
+  /// @tparam Callable The compile-time member function pointer
+  /// @tparam Type The type of the instance the member function should be called on
+  /// @param instance The instance on which the member function pointer should be called on
+  /// @note @c Delegate does not assume owner ship over @p instance.
+  /// @note @c DelegateFuncTag is used to communicate the callable type
+  template <auto Callable, typename Type, DelegateType T = kOwnership,
+            typename = std::enable_if_t<T == DelegateType::NonOwning>>
+  Delegate(DelegateFuncTag<Callable>, const Type *instance) {
+    connect<Callable>(instance);
+  }
+
   /// Constructor from rvalue reference is deleted, should catch construction
   /// with temporary objects and thus invalid pointers
   template <typename Callable, typename = isNoFunPtr<Callable>>

Tests/UnitTests/Core/Utilities/DelegateTests.cpp

@@ -126,6 +126,21 @@ BOOST_AUTO_TEST_CASE(ConnectRuntime) {
   }
 }
 
+BOOST_AUTO_TEST_CASE(ConnectConstructFuncPtr) {
+  Delegate<int(int, int)> add{DelegateFuncTag<&sumImpl>{}};
+  BOOST_CHECK(add);
+  BOOST_CHECK(add.connected());
+  BOOST_CHECK_EQUAL(add(4, 4), 8);
+
+  Subtractor s{18};
+  Delegate<int(int)> sub{DelegateFuncTag<&Subtractor::execute>{}, &s};
+
+  BOOST_CHECK(sub);
+  BOOST_CHECK(sub.connected());
+
+  BOOST_CHECK_EQUAL(sub(7), 7 - 18);
+}
+
 void modify(int& v, int a) {
   v = a;
 }