From ff0bbc2e0517bdb724e05ddbcee69013ee78072c Mon Sep 17 00:00:00 2001
From: Giulio Eulisse <10544+ktf@users.noreply.github.com>
Date: Wed, 9 Jun 2021 11:50:24 +0200
Subject: [PATCH] DPL: extend call_if_defined to have a fallback if not defined

---
 Framework/Core/CMakeLists.txt                 |  1 +
 Framework/Core/test/test_CheckTypes.cxx       | 45 +++++++++++++++++++
 .../Foundation/include/Framework/CheckTypes.h | 17 +++++--
 3 files changed, 59 insertions(+), 4 deletions(-)
 create mode 100644 Framework/Core/test/test_CheckTypes.cxx

diff --git a/Framework/Core/CMakeLists.txt b/Framework/Core/CMakeLists.txt
index 7bee2f9f02682..d40108210260d 100644
--- a/Framework/Core/CMakeLists.txt
+++ b/Framework/Core/CMakeLists.txt
@@ -153,6 +153,7 @@ foreach(t
         ConfigurationOptionsRetriever
         CallbackRegistry
         ChannelSpecHelpers
+        CheckTypes
         CompletionPolicy
         ComputingResourceHelpers
         ConfigParamStore
diff --git a/Framework/Core/test/test_CheckTypes.cxx b/Framework/Core/test/test_CheckTypes.cxx
new file mode 100644
index 0000000000000..f884f117e9ba3
--- /dev/null
+++ b/Framework/Core/test/test_CheckTypes.cxx
@@ -0,0 +1,45 @@
+// Copyright CERN and copyright holders of ALICE O2. This software is
+// distributed under the terms of the GNU General Public License v3 (GPL
+// Version 3), copied verbatim in the file "COPYING".
+//
+// See http://alice-o2.web.cern.ch/license for full licensing information.
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+#define BOOST_TEST_MODULE Test Framework Traits
+#define BOOST_TEST_MAIN
+#define BOOST_TEST_DYN_LINK
+
+#include <boost/test/unit_test.hpp>
+#include "Framework/CheckTypes.h"
+
+using namespace o2::framework;
+
+struct Foo {
+  bool foo;
+};
+
+BOOST_AUTO_TEST_CASE(CallIfUndefined)
+{
+  bool shouldBeCalled = false;
+  bool shouldNotBeCalled = false;
+  bool shouldBeCalledOnUndefined = false;
+
+  call_if_defined<struct Foo>([&shouldBeCalled](auto) { shouldBeCalled = true; });
+  call_if_defined<struct Bar>([&shouldNotBeCalled](auto) { shouldNotBeCalled = true; });
+  BOOST_REQUIRE_EQUAL(shouldBeCalled, true);
+  BOOST_REQUIRE_EQUAL(shouldNotBeCalled, false);
+
+  shouldBeCalled = false;
+  shouldNotBeCalled = false;
+  shouldBeCalledOnUndefined = false;
+
+  call_if_defined_full<struct Bar>([&shouldNotBeCalled](auto) { shouldNotBeCalled = true; }, []() {});
+  BOOST_REQUIRE_EQUAL(shouldNotBeCalled, false);
+  BOOST_REQUIRE_EQUAL(shouldBeCalledOnUndefined, false);
+  call_if_defined_full<struct Bar>([&shouldNotBeCalled](auto) { shouldNotBeCalled = true; }, [&shouldBeCalledOnUndefined]() { shouldBeCalledOnUndefined = true; });
+  BOOST_REQUIRE_EQUAL(shouldNotBeCalled, false);
+  BOOST_REQUIRE_EQUAL(shouldBeCalledOnUndefined, true);
+}
diff --git a/Framework/Foundation/include/Framework/CheckTypes.h b/Framework/Foundation/include/Framework/CheckTypes.h
index 681a787d071b9..fac3ad26bd81d 100644
--- a/Framework/Foundation/include/Framework/CheckTypes.h
+++ b/Framework/Foundation/include/Framework/CheckTypes.h
@@ -21,16 +21,25 @@ constexpr bool is_type_complete_v = false;
 template <typename T>
 constexpr bool is_type_complete_v<T, std::void_t<decltype(sizeof(T))>> = true;
 
-/// Helper which will invoke lambda if the type T is actually available.
+/// Helper which will invoke @a onDefined if the type T is actually available
+/// or @a onUndefined if the type T is a forward declaration.
 /// Can be used to check for existence or not of a given type.
-template <typename T, typename TLambda>
-void call_if_defined(TLambda&& lambda)
+template <typename T, typename TDefined, typename TUndefined>
+void call_if_defined_full(TDefined&& onDefined, TUndefined&& onUndefined)
 {
   if constexpr (is_type_complete_v<T>) {
-    lambda(static_cast<T*>(nullptr));
+    onDefined(static_cast<T*>(nullptr));
+  } else {
+    onUndefined();
   }
 }
 
+template <typename T, typename TDefined>
+void call_if_defined(TDefined&& onDefined)
+{
+  call_if_defined_full<T>(onDefined, []() -> void {});
+}
+
 } // namespace o2::framework
 
 #endif // O2_FRAMEWORK_CHECKTYPES_H_