From 35f0231fe83ebee43f60d476a41e965f79a4cfa3 Mon Sep 17 00:00:00 2001
From: Paul Gessinger <hello@paulgessinger.com>
Date: Wed, 9 Oct 2024 10:46:58 +0200
Subject: [PATCH 1/2] feat(util): Add `overloaded` helper

This is useful in combination with `std::visit`.
---
 Core/include/Acts/Utilities/Helpers.hpp         | 17 +++++++++++++++++
 Tests/UnitTests/Core/Utilities/HelpersTests.cpp | 14 ++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/Core/include/Acts/Utilities/Helpers.hpp b/Core/include/Acts/Utilities/Helpers.hpp
index 4bf9d1c89c3..c59555fd848 100644
--- a/Core/include/Acts/Utilities/Helpers.hpp
+++ b/Core/include/Acts/Utilities/Helpers.hpp
@@ -204,4 +204,21 @@ bool rangeContainsValue(const R& range, const T& value) {
   return std::ranges::find(range, value) != std::ranges::end(range);
 }
 
+/// Helper struct that can turn a set of lambdas into a single entity with
+/// overloaded call operator. This can be useful for example in a std::visit
+/// call.
+/// ```cpp
+/// std::visit(overloaded{
+///  [](const int& i) { std::cout << "int: " << i << std::endl; },
+///  [](const std::string& s) { std::cout << "string: " << s << std::endl; },
+/// }, variant);
+/// ```
+template <class... Ts>
+struct overloaded : Ts... {
+  using Ts::operator()...;
+};
+
+template <class... Ts>
+overloaded(Ts...) -> overloaded<Ts...>;
+
 }  // namespace Acts
diff --git a/Tests/UnitTests/Core/Utilities/HelpersTests.cpp b/Tests/UnitTests/Core/Utilities/HelpersTests.cpp
index 68f173db492..f6252b82482 100644
--- a/Tests/UnitTests/Core/Utilities/HelpersTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/HelpersTests.cpp
@@ -297,6 +297,20 @@ BOOST_AUTO_TEST_CASE(incidentAnglesTest) {
   }
 }
 
+BOOST_AUTO_TEST_CASE(Overloaded) {
+  struct A {};
+  std::variant<int, double, A> var;
+
+  var = 42;
+
+  std::visit(overloaded{
+                 [](int) { BOOST_CHECK(true); },
+                 [](double) { BOOST_CHECK(false); },
+                 [](A) { BOOST_CHECK(false); },
+             },
+             var);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }  // namespace Acts::Test

From a93a7c5196de0113d91e24b849c0b6ba6ed9f298 Mon Sep 17 00:00:00 2001
From: Paul Gessinger <hello@paulgessinger.com>
Date: Wed, 6 Nov 2024 18:07:23 +0100
Subject: [PATCH 2/2] fix missing include

---
 Tests/UnitTests/Core/Utilities/HelpersTests.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Tests/UnitTests/Core/Utilities/HelpersTests.cpp b/Tests/UnitTests/Core/Utilities/HelpersTests.cpp
index f6252b82482..aa5e011669d 100644
--- a/Tests/UnitTests/Core/Utilities/HelpersTests.cpp
+++ b/Tests/UnitTests/Core/Utilities/HelpersTests.cpp
@@ -26,6 +26,7 @@
 #include <string>
 #include <tuple>
 #include <utility>
+#include <variant>
 #include <vector>
 
 using namespace Acts::VectorHelpers;