From aad0dabebe2b6cfdf3935be46148651592ad64b4 Mon Sep 17 00:00:00 2001
From: John Wellbelove <jwellbelove@users.noreply.github.com>
Date: Tue, 22 Mar 2022 15:16:51 +0000
Subject: [PATCH] Re-initroduced etl::functor

Added constexpr to etl::member_function_wrapper and etl:;functor_wrapper
---
 include/etl/utility.h | 45 ++++++++++++++++++++++++++++++++++++++-----
 test/test_utility.cpp | 37 +++++++++++++++++++++--------------
 2 files changed, 63 insertions(+), 19 deletions(-)

diff --git a/include/etl/utility.h b/include/etl/utility.h
index e8262975..7d985f82 100644
--- a/include/etl/utility.h
+++ b/include/etl/utility.h
@@ -444,7 +444,39 @@ namespace etl
   typename etl::add_rvalue_reference<T>::type declval() ETL_NOEXCEPT;
 #endif
 
+#if ETL_USING_CPP11
+  //*************************************************************************
+  /// A function wrapper for free/global functions.
+  //*************************************************************************
+  template <typename TReturn, typename... TParams>
+  class functor
+  {
+  public:
 
+    //*********************************
+    /// Constructor.
+    //*********************************
+    constexpr functor(TReturn(*ptr_)(TParams...))
+      : ptr(ptr_)
+    {
+    }
+
+    //*********************************
+    /// Const function operator.
+    //*********************************
+    constexpr TReturn operator()(TParams... args) const
+    {
+      return ptr(etl::forward<TParams>(args)...);
+    }
+
+  private:
+
+    /// The pointer to the function.
+    TReturn(*ptr)(TParams...);
+  };
+#endif
+
+#if ETL_USING_CPP11
   //*****************************************************************************
   // A wrapper for a member function
   // Creates a static member function that calls the specified member function.
@@ -458,12 +490,14 @@ namespace etl
   public:
 
     template <typename T, T& Instance, TReturn(T::* Method)(TParams...)>
-    static TReturn function(TParams... params)
+    static constexpr TReturn function(TParams... params)
     {
-      return (Instance.*Method)(std::forward<TParams>(params)...);
+      return (Instance.*Method)(etl::forward<TParams>(params)...);
     }
   };
+#endif
 
+#if ETL_USING_CPP11
   //*****************************************************************************
   // A wrapper for a functor
   // Creates a static member function that calls the specified functor.
@@ -476,12 +510,13 @@ namespace etl
   {
   public:
 
-    template <typename TDelegate, TDelegate& Instance>
-    static TReturn function(TParams... params)
+    template <typename TFunctor, TFunctor& Instance>
+    static constexpr TReturn function(TParams... params)
     {
-      return Instance(std::forward<TParams>(params)...);
+      return Instance(etl::forward<TParams>(params)...);
     }
   };
+#endif
 }
 
 #endif
diff --git a/test/test_utility.cpp b/test/test_utility.cpp
index 0d294564..a2cad4be 100644
--- a/test/test_utility.cpp
+++ b/test/test_utility.cpp
@@ -36,6 +36,7 @@ namespace
 {
   bool nonConstCalled;
   bool constCalled;
+  int  value;
 
   void TestText(std::string&)
   {
@@ -47,6 +48,11 @@ namespace
     constCalled = true;
   }
 
+  int TestGlobal(int i)
+  {
+    return 2 * i;
+  }
+
   using ItemM1 = TestDataM<int>;
   using ItemM2 = TestDataM<double>;
 
@@ -56,17 +62,15 @@ namespace
   {
   public:
 
-    void MemberFunction(int i)
+    int MemberFunction(int i)
     {
-      value  = i;
+      return 2 * i;
     }
 
-    void operator()(int i)
+    int operator()(int i)
     {
-      value = i;
+      return 2 * i;
     }
-
-    int value;
   };
 
   static TestClass test;
@@ -325,24 +329,29 @@ namespace
       CHECK(constCalled);
     }
 
+    //*************************************************************************
+    TEST(test_functor)
+    {
+      constexpr auto ptr = TestGlobal;
+
+      constexpr etl::functor fw1(ptr);
+      CHECK_EQUAL(2, fw1(1));
+    }
+
     //*************************************************************************
     TEST(test_member_function_wrapper)
     {
-      void(*pf)(int) = &etl::member_function_wrapper<void(int)>::function<TestClass, test, &TestClass::MemberFunction>;
+      constexpr int(*pf)(int) = &etl::member_function_wrapper<int(int)>::function<TestClass, test, &TestClass::MemberFunction>;
 
-      test.value = 0;
-      pf(1);
-      CHECK_EQUAL(1, test.value);
+      CHECK_EQUAL(2, pf(1));
     }
 
     //*************************************************************************
     TEST(test_functor_wrapper)
     {
-      void(*pf)(int) = &etl::functor_wrapper<void(int)>::function<TestClass, test>;
+      constexpr int(*pf)(int) = &etl::functor_wrapper<int(int)>::function<TestClass, test>;
 
-      test.value = 0;
-      pf(1);
-      CHECK_EQUAL(1, test.value);
+      CHECK_EQUAL(2, pf(1));
     }
   };
 }