etl/delegate: fix accident creation of a delegate to an rvalue delegate when copying/assigning from delegate with mismatching signature

Author: VladimirP1

include/etl/private/delegate_cpp11.h

@@ -86,13 +86,24 @@ namespace etl
   //*************************************************************************
   /// Declaration.
   //*************************************************************************
-  template <typename T> class delegate;
+  template <typename T>
+  class delegate;
+
+  //*************************************************************************
+  /// Specialisation - base class of all delegates.
+  //*************************************************************************
+  template <>
+  class delegate<void>
+  {
+  protected:
+    delegate() = default;
+  };
 
   //*************************************************************************
   /// Specialisation.
   //*************************************************************************
   template <typename TReturn, typename... TParams>
-  class delegate<TReturn(TParams...)> final
+  class delegate<TReturn(TParams...)> final : public delegate<void>
   {
   public:
 
@@ -111,7 +122,7 @@ namespace etl
     //*************************************************************************
     // Construct from lambda or functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_CONSTEXPR14 delegate(TLambda& instance)
     {
       assign((void*)(&instance), lambda_stub<TLambda>);
@@ -120,7 +131,7 @@ namespace etl
     //*************************************************************************
     // Construct from const lambda or functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_CONSTEXPR14 delegate(const TLambda& instance)
     {
       assign((void*)(&instance), const_lambda_stub<TLambda>);
@@ -139,7 +150,7 @@ namespace etl
     //*************************************************************************
     /// Create from Lambda or Functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_NODISCARD
     static ETL_CONSTEXPR14 delegate create(TLambda& instance)
     {
@@ -149,7 +160,7 @@ namespace etl
     //*************************************************************************
     /// Create from const Lambda or Functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_NODISCARD
       static ETL_CONSTEXPR14 delegate create(const TLambda& instance)
     {
@@ -257,7 +268,7 @@ namespace etl
     //*************************************************************************
     /// Set from Lambda or Functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_CONSTEXPR14 void set(TLambda& instance)
     {
       assign((void*)(&instance), lambda_stub<TLambda>);
@@ -266,7 +277,7 @@ namespace etl
     //*************************************************************************
     /// Set from const Lambda or Functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_CONSTEXPR14 void set(const TLambda& instance)
     {
       assign((void*)(&instance), const_lambda_stub<TLambda>);
@@ -427,7 +438,7 @@ namespace etl
     //*************************************************************************
     /// Create from Lambda or Functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_CONSTEXPR14 delegate& operator =(TLambda& instance)
     {
       assign((void*)(&instance), lambda_stub<TLambda>);
@@ -437,7 +448,7 @@ namespace etl
     //*************************************************************************
     /// Create from const Lambda or Functor.
     //*************************************************************************
-    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TParams...)>, TLambda>::value, void>>
+    template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value && !std::is_base_of<delegate<void>, TLambda>::value, void>>
     ETL_CONSTEXPR14 delegate& operator =(const TLambda& instance)
     {
       assign((void*)(&instance), const_lambda_stub<TLambda>);