delegate_cpp11.h

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/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2019 John Wellbelove
 
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of this software and associated documentation files(the "Software"), to deal
in the Software without restriction, including without limitation the rights
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copies or substantial portions of the Software.
 
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/******************************************************************************
 
Copyright (C) 2017 by Sergey A Kryukov: derived work
http://www.SAKryukov.org
http://www.codeproject.com/Members/SAKryukov
 
Based on original work by Sergey Ryazanov:
"The Impossibly Fast C++ Delegates", 18 Jul 2005
https://www.codeproject.com/articles/11015/the-impossibly-fast-c-delegates
 
MIT license:
http://en.wikipedia.org/wiki/MIT_License
 
Original publication:
https://www.codeproject.com/Articles/1170503/The-Impossibly-Fast-Cplusplus-Delegates-Fixed
 
******************************************************************************/
 
#ifndef ETL_DELEGATE_CPP11_INCLUDED
#define ETL_DELEGATE_CPP11_INCLUDED
 
#include "../platform.h"
#include "../error_handler.h"
#include "../exception.h"
#include "../function_traits.h"
#include "../optional.h"
#include "../type_list.h"
#include "../type_traits.h"
#include "../utility.h"
 
namespace etl
{
  //***************************************************************************
  //***************************************************************************
  class delegate_exception : public exception
  {
  public:
 
    delegate_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
      : exception(reason_, file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class delegate_uninitialised : public delegate_exception
  {
  public:
 
    delegate_uninitialised(string_type file_name_, numeric_type line_number_)
      : delegate_exception(ETL_ERROR_TEXT("delegate:uninitialised", ETL_DELEGATE_FILE_ID"A"), file_name_, line_number_)
    {
    }
  };
 
  //*****************************************************************
  //*****************************************************************
  struct delegate_tag
  {
  };
 
  //***************************************************************************
  //***************************************************************************
  template <typename T>
  struct is_delegate : etl::bool_constant<etl::is_base_of<delegate_tag, T>::value>
  {
  };
 
#if ETL_USING_CPP17
  template <typename T>
  inline constexpr bool is_delegate_v = is_delegate<T>::value;
#endif
 
  //*************************************************************************
  //*************************************************************************
  template <typename T>
  class delegate;
 
  //*************************************************************************
  //*************************************************************************
  template <typename TReturn, typename... TArgs>
  class delegate<TReturn(TArgs...)> final : public delegate_tag
  {
  private:

    using object_ptr = void*;

    using function_ptr = TReturn (*)(TArgs...);
 
  public:

    using return_type = TReturn;

    using argument_types = etl::type_list<TArgs...>;
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 delegate() ETL_NOEXCEPT
    {
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 delegate(const delegate& other) = default;
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_CONSTEXPR14 delegate(TLambda& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), lambda_stub<TLambda>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_CONSTEXPR14 delegate(const TLambda& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), const_lambda_stub<TLambda>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TLambda,
              typename = etl::enable_if_t<etl::is_class<TLambda>::value && !etl::is_same<etl::delegate<TReturn(TArgs...)>, TLambda>::value
                                            && !etl::is_convertible<TLambda, function_ptr>::value,
                                          void>>
    ETL_CONSTEXPR14 delegate(TLambda&& instance) = delete;
 
    //*************************************************************************
    //*************************************************************************
    explicit ETL_CONSTEXPR14 delegate(function_ptr fp) ETL_NOEXCEPT
      : invocation(fp, function_ptr_stub)
    {
    }
 
    //*************************************************************************
    //*************************************************************************
    template <TReturn (*Method)(TArgs...)>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create() ETL_NOEXCEPT
    {
      return delegate(function_stub<Method>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create(TLambda& instance) ETL_NOEXCEPT
    {
      return delegate(object_ptr(&instance), lambda_stub<TLambda>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create(const TLambda& instance) ETL_NOEXCEPT
    {
      return delegate(object_ptr(&instance), const_lambda_stub<TLambda>);
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create(function_ptr fp) ETL_NOEXCEPT
    {
      return delegate(fp, function_ptr_stub);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...)>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create(T& instance) ETL_NOEXCEPT
    {
      return delegate(object_ptr(&instance), method_stub<T, Method>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...)>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create(T&& instance) = delete;
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create(const T& instance) ETL_NOEXCEPT
    {
      return delegate(object_ptr(&instance), const_method_stub<T, Method>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const>
    static ETL_CONSTEXPR14 delegate create(T&& instance) = delete;
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, T& Instance, TReturn (T::*Method)(TArgs...)>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create() ETL_NOEXCEPT
    {
      return delegate(method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...), T& Instance>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create() ETL_NOEXCEPT
    {
      return delegate(method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, T const& Instance, TReturn (T::*Method)(TArgs...) const>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create() ETL_NOEXCEPT
    {
      return delegate(const_method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const, T const& Instance>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create() ETL_NOEXCEPT
    {
      return delegate(const_method_instance_stub<T, Method, Instance>);
    }
 
#if !(defined(ETL_COMPILER_GCC) && (__GNUC__ <= 8))
    //*************************************************************************
    //*************************************************************************
    template <typename T, T& Instance>
    ETL_NODISCARD
    static ETL_CONSTEXPR14 delegate create() ETL_NOEXCEPT
    {
      return delegate(operator_instance_stub<T, Instance>);
    }
#endif
 
    //*************************************************************************
    //*************************************************************************
    template <TReturn (*Method)(TArgs...)>
    ETL_CONSTEXPR14 void set() ETL_NOEXCEPT
    {
      assign(function_stub<Method>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_CONSTEXPR14 void set(TLambda& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), lambda_stub<TLambda>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_CONSTEXPR14 void set(const TLambda& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), const_lambda_stub<TLambda>);
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 void set(function_ptr fp) ETL_NOEXCEPT
    {
      assign(fp, function_ptr_stub);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...)>
    ETL_CONSTEXPR14 void set(T& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), method_stub<T, Method>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const>
    ETL_CONSTEXPR14 void set(T& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), const_method_stub<T, Method>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, T& Instance, TReturn (T::*Method)(TArgs...)>
    ETL_CONSTEXPR14 void set() ETL_NOEXCEPT
    {
      assign(method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...), T& Instance>
    ETL_CONSTEXPR14 void set() ETL_NOEXCEPT
    {
      assign(method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, T const& Instance, TReturn (T::*Method)(TArgs...) const>
    ETL_CONSTEXPR14 void set() ETL_NOEXCEPT
    {
      assign(const_method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const, T const& Instance>
    ETL_CONSTEXPR14 void set() ETL_NOEXCEPT
    {
      assign(const_method_instance_stub<T, Method, Instance>);
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 void clear() ETL_NOEXCEPT
    {
      invocation.clear();
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename... TCallArgs>
    ETL_CONSTEXPR14 return_type operator()(TCallArgs&&... args) const
    {
      ETL_STATIC_ASSERT((sizeof...(TCallArgs) == sizeof...(TArgs)), "Incorrect number of parameters passed to delegate");
      ETL_STATIC_ASSERT((etl::type_lists_are_convertible<etl::type_list<TCallArgs&&...>, argument_types>::value),
                        "Incompatible parameter types passed to delegate");
 
      ETL_ASSERT(is_valid(), ETL_ERROR(delegate_uninitialised));
 
      return (*invocation.stub)(invocation, etl::forward<TCallArgs>(args)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TRet = TReturn, typename... TCallArgs>
    ETL_CONSTEXPR14 typename etl::enable_if_t<etl::is_same<TRet, void>::value, bool> call_if(TCallArgs&&... args) const
    {
      ETL_STATIC_ASSERT((sizeof...(TCallArgs) == sizeof...(TArgs)), "Incorrect number of parameters passed to delegate");
      ETL_STATIC_ASSERT((etl::type_lists_are_convertible<etl::type_list<TCallArgs&&...>, argument_types>::value),
                        "Incompatible parameter types passed to delegate");
 
      if (is_valid())
      {
        (*invocation.stub)(invocation, etl::forward<TCallArgs>(args)...);
        return true;
      }
      else
      {
        return false;
      }
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TRet = TReturn, typename... TCallArgs>
    ETL_CONSTEXPR14 typename etl::enable_if_t<!etl::is_same<TRet, void>::value, etl::optional<TReturn>> call_if(TCallArgs&&... args) const
    {
      ETL_STATIC_ASSERT((sizeof...(TCallArgs) == sizeof...(TArgs)), "Incorrect number of parameters passed to delegate");
      ETL_STATIC_ASSERT((etl::type_lists_are_convertible<etl::type_list<TCallArgs&&...>, argument_types>::value),
                        "Incompatible parameter types passed to delegate");
 
      etl::optional<TReturn> result;
 
      if (is_valid())
      {
        result = (*invocation.stub)(invocation, etl::forward<TCallArgs>(args)...);
      }
 
      return result;
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TAlternative, typename... TCallArgs>
    ETL_CONSTEXPR14 TReturn call_or(TAlternative&& alternative, TCallArgs&&... args) const
    {
      ETL_STATIC_ASSERT((sizeof...(TCallArgs) == sizeof...(TArgs)), "Incorrect number of parameters passed to delegate");
      ETL_STATIC_ASSERT((etl::type_lists_are_convertible<etl::type_list<TCallArgs&&...>, argument_types>::value),
                        "Incompatible parameter types passed to delegate");
 
      if (is_valid())
      {
        return (*invocation.stub)(invocation, etl::forward<TCallArgs>(args)...);
      }
      else
      {
        return etl::forward<TAlternative>(alternative)(etl::forward<TCallArgs>(args)...);
      }
    }
 
    //*************************************************************************
    //*************************************************************************
    template <TReturn (*Method)(TArgs...), typename... TCallArgs>
    ETL_CONSTEXPR14 TReturn call_or(TCallArgs&&... args) const
    {
      ETL_STATIC_ASSERT((sizeof...(TCallArgs) == sizeof...(TArgs)), "Incorrect number of parameters passed to delegate");
      ETL_STATIC_ASSERT((etl::type_lists_are_convertible<etl::type_list<TCallArgs&&...>, argument_types>::value),
                        "Incompatible parameter types passed to delegate");
 
      if (is_valid())
      {
        return (*invocation.stub)(invocation, etl::forward<TCallArgs>(args)...);
      }
      else
      {
        return (Method)(etl::forward<TCallArgs>(args)...);
      }
    }
 
    //*************************************************************************
    //*************************************************************************
    delegate& operator=(const delegate& rhs) = default;
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_CONSTEXPR14 delegate& operator=(TLambda& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), lambda_stub<TLambda>);
      return *this;
    }
 
    //*************************************************************************
    //*************************************************************************
    template < typename TLambda, typename = etl::enable_if_t< etl::is_class<TLambda>::value && !is_delegate<TLambda>::value, void>>
    ETL_CONSTEXPR14 delegate& operator=(const TLambda& instance) ETL_NOEXCEPT
    {
      assign(object_ptr(&instance), const_lambda_stub<TLambda>);
      return *this;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 delegate& operator=(function_ptr fp) ETL_NOEXCEPT
    {
      if (fp == ETL_NULLPTR)
      {
        invocation.clear();
      }
      else
      {
        assign(fp, function_ptr_stub);
      }
      return *this;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_NODISCARD ETL_CONSTEXPR14 bool operator==(const delegate& rhs) const ETL_NOEXCEPT
    {
      return invocation == rhs.invocation;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 bool operator!=(const delegate& rhs) const ETL_NOEXCEPT
    {
      return invocation != rhs.invocation;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_NODISCARD ETL_CONSTEXPR14 bool is_valid() const ETL_NOEXCEPT
    {
      // GCC's UBSan instruments function pointer comparisons, which prevents
      // constexpr evaluation. Use implicit bool conversion at compile time
      // to avoid the instrumented != comparison while still checking validity.
      if (etl::is_constant_evaluated())
      {
        return static_cast<bool>(invocation.stub);
      }
 
      return invocation.stub != ETL_NULLPTR;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_NODISCARD ETL_CONSTEXPR14 operator bool() const ETL_NOEXCEPT
    {
      return is_valid();
    }
 
  private:
 
    //*************************************************************************
    // Callable compatibility: detects if C (or const C) is invocable with
    // (TArgs...) and returns a type convertible to TReturn. Works with generic
    // lambdas and functors.
    template <typename TCallableType, typename = void>
    struct is_invocable_with : etl::false_type
    {
    };
 
    template <typename TCallableType>
    struct is_invocable_with< TCallableType, etl::void_t<decltype(etl::declval<TCallableType&>()(etl::declval<TArgs>()...))>>
      : etl::bool_constant< etl::is_convertible< decltype(etl::declval<TCallableType&>()(etl::declval<TArgs>()...)), TReturn>::value>
    {
    };
 
    template <typename TCallableType, typename = void>
    struct is_invocable_with_const : etl::false_type
    {
    };
 
    template <typename TCallableType>
    struct is_invocable_with_const< TCallableType, etl::void_t<decltype(etl::declval<const TCallableType&>()(etl::declval<TArgs>()...))>>
      : etl::bool_constant< etl::is_convertible< decltype(etl::declval<const TCallableType&>()(etl::declval<TArgs>()...)), TReturn>::value>
    {
    };
 
    template <typename TCallableType>
    struct is_compatible_callable : etl::bool_constant<is_invocable_with<TCallableType>::value || is_invocable_with_const<TCallableType>::value>
    {
    };
 
    //*************************************************************************
    //*************************************************************************
    struct invocation_element
    {
      using stub_type = TReturn (*)(const invocation_element&, TArgs...);
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 invocation_element() ETL_NOEXCEPT
        : ptr(object_ptr(ETL_NULLPTR))
        , stub(ETL_NULLPTR)
      {
      }
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 invocation_element(stub_type stub_) ETL_NOEXCEPT
        : ptr()
        , stub(stub_)
      {
      }
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 invocation_element(object_ptr object_, stub_type stub_) ETL_NOEXCEPT
        : ptr(object_)
        , stub(stub_)
      {
      }
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 invocation_element(function_ptr fp_, stub_type stub_) ETL_NOEXCEPT
        : ptr(fp_)
        , stub(stub_)
      {
      }
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 bool operator==(const invocation_element& rhs) const ETL_NOEXCEPT
      {
        return (rhs.stub == stub) && ((stub == function_ptr_stub) ? (rhs.ptr.fp == ptr.fp) : (rhs.ptr.object == ptr.object));
      }
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 bool operator!=(const invocation_element& rhs) const ETL_NOEXCEPT
      {
        return !operator==(rhs);
      }
 
      //***********************************************************************
      //***********************************************************************
      ETL_CONSTEXPR14 void clear() ETL_NOEXCEPT
      {
        stub = ETL_NULLPTR;
      }
 
      //***********************************************************************
      //***********************************************************************
      union ptr_type
      {
        ETL_CONSTEXPR14 ptr_type() ETL_NOEXCEPT
          : object(ETL_NULLPTR)
        {
        }

        ETL_CONSTEXPR14 ptr_type(object_ptr object_) ETL_NOEXCEPT
          : object(object_)
        {
        }

        ETL_CONSTEXPR14 ptr_type(function_ptr fp_) ETL_NOEXCEPT
          : fp(fp_)
        {
        }
 
        object_ptr   object;
        function_ptr fp;
      };
 
      ptr_type  ptr;
      stub_type stub;
    };

    using stub_type = typename invocation_element::stub_type;
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 delegate(object_ptr object, stub_type stub) ETL_NOEXCEPT
      : invocation(object, stub)
    {
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 delegate(function_ptr fp, stub_type stub) ETL_NOEXCEPT
      : invocation(fp, stub)
    {
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 delegate(stub_type stub) ETL_NOEXCEPT
      : invocation(stub)
    {
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 void assign(object_ptr object, stub_type stub) ETL_NOEXCEPT
    {
      invocation.ptr.object = object;
      invocation.stub       = stub;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 void assign(function_ptr fp, stub_type stub) ETL_NOEXCEPT
    {
      invocation.ptr.fp = fp;
      invocation.stub   = stub;
    }
 
    //*************************************************************************
    //*************************************************************************
    ETL_CONSTEXPR14 void assign(stub_type stub) ETL_NOEXCEPT
    {
      invocation.ptr.object = ETL_NULLPTR;
      invocation.stub       = stub;
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...)>
    static ETL_CONSTEXPR14 TReturn method_stub(const invocation_element& invocation, TArgs... args)
    {
      T* p = static_cast<T*>(invocation.ptr.object);
      return (p->*Method)(etl::forward<TArgs>(args)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const>
    static ETL_CONSTEXPR14 TReturn const_method_stub(const invocation_element& invocation, TArgs... args)
    {
      T* const p = static_cast<T*>(invocation.ptr.object);
      return (p->*Method)(etl::forward<TArgs>(args)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...), T& Instance>
    static ETL_CONSTEXPR14 TReturn method_instance_stub(const invocation_element&, TArgs... args)
    {
      return (Instance.*Method)(etl::forward<TArgs>(args)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename T, TReturn (T::*Method)(TArgs...) const, const T& Instance>
    static ETL_CONSTEXPR14 TReturn const_method_instance_stub(const invocation_element&, TArgs... args)
    {
      return (Instance.*Method)(etl::forward<TArgs>(args)...);
    }
 
#if !(defined(ETL_COMPILER_GCC) && (__GNUC__ <= 8))
    //*************************************************************************
    //*************************************************************************
    template <typename T, T& Instance>
    static ETL_CONSTEXPR14 TReturn operator_instance_stub(const invocation_element&, TArgs... args)
    {
      return Instance.operator()(etl::forward<TArgs>(args)...);
    }
#endif
 
    //*************************************************************************
    //*************************************************************************
    template <TReturn (*Method)(TArgs...)>
    static ETL_CONSTEXPR14 TReturn function_stub(const invocation_element&, TArgs... args)
    {
      return (Method)(etl::forward<TArgs>(args)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    static TReturn function_ptr_stub(const invocation_element& invocation, TArgs... args)
    {
      return invocation.ptr.fp(etl::forward<TArgs>(args)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TLambda>
    static ETL_CONSTEXPR14 TReturn lambda_stub(const invocation_element& invocation, TArgs... arg)
    {
      ETL_STATIC_ASSERT(is_compatible_callable<TLambda>::value, "etl::delegate: bound lambda/functor is not compatible with the delegate signature");
 
      TLambda* p = static_cast<TLambda*>(invocation.ptr.object);
      return (p->operator())(etl::forward<TArgs>(arg)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    template <typename TLambda>
    static ETL_CONSTEXPR14 TReturn const_lambda_stub(const invocation_element& invocation, TArgs... arg)
    {
      ETL_STATIC_ASSERT(is_compatible_callable<TLambda>::value, "etl::delegate: bound lambda/functor is not compatible with the delegate signature");
 
      const TLambda* p = static_cast<const TLambda*>(invocation.ptr.object);
      return (p->operator())(etl::forward<TArgs>(arg)...);
    }
 
    //*************************************************************************
    //*************************************************************************
    invocation_element invocation;
  };
 
#if ETL_USING_CPP17
  //*************************************************************************
  //*************************************************************************
  template <auto Function>
  ETL_NODISCARD
  constexpr auto make_delegate() ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits<decltype(Function)>::function_type;
 
    return etl::delegate<function_type>::template create<Function>();
  }
 
  //*************************************************************************
  //*************************************************************************
  template <typename TLambda, typename = etl::enable_if_t<etl::is_class<TLambda>::value, void>>
  ETL_NODISCARD
  constexpr auto make_delegate(TLambda& instance) ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits< decltype(&TLambda::operator())>::function_type;
 
    return etl::delegate<function_type>(instance);
  }
 
  //*************************************************************************
  //*************************************************************************
  template <typename T, T& Instance>
  ETL_NODISCARD
  constexpr auto make_delegate() ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits<decltype(&T::operator())>::function_type;
 
    return etl::delegate<function_type>::template create<T, Instance>();
  }
 
  //*************************************************************************
  //*************************************************************************
  template <typename T, auto Method, T& Instance, typename = etl::enable_if_t< !etl::function_traits<decltype(Method)>::is_const>>
  ETL_NODISCARD
  constexpr auto make_delegate() ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits<decltype(Method)>::function_type;
 
    return etl::delegate<function_type>::template create<T, Method, Instance>();
  }
 
  //*************************************************************************
  //*************************************************************************
  template <typename T, auto Method, const T& Instance, typename = etl::enable_if_t< etl::function_traits<decltype(Method)>::is_const>>
  ETL_NODISCARD
  constexpr auto make_delegate() ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits<decltype(Method)>::function_type;
 
    return etl::delegate<function_type>::template create<T, Method, Instance>();
  }
 
  //*************************************************************************
  //*************************************************************************
  template <typename T, auto Method>
  ETL_NODISCARD
  constexpr auto make_delegate(T& instance) ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits<decltype(Method)>::function_type;
 
    return etl::delegate<function_type>::template create<T, Method>(instance);
  }
 
  //*************************************************************************
  //*************************************************************************
  template <typename T, auto Method>
  ETL_NODISCARD
  constexpr auto make_delegate(const T& instance) ETL_NOEXCEPT
  {
    using function_type = typename etl::function_traits<decltype(Method)>::function_type;
 
    return etl::delegate<function_type>::template create<T, Method>(instance);
  }
#endif
} // namespace etl
 
#endif