function_traits.h

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/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
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Copyright(c) 2025 John Wellbelove
 
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#ifndef ETL_FUNCTION_TRAITS_INCLUDED
#define ETL_FUNCTION_TRAITS_INCLUDED
 
#include "platform.h"
#include "type_list.h"
#include "type_traits.h"
 
#if ETL_USING_CPP11
 
namespace etl
{
  //***************************************************************************
  // Primary template (unspecialized)
  //***************************************************************************
  template <typename T, typename Enable = void>
  struct function_traits;
 
  //***************************************************************************
  // Base for plain function type TReturn(TArgs...)
  //***************************************************************************
  template <typename TReturn, typename... TArgs>
  struct function_traits<TReturn(TArgs...), void>
  {
  public:
 
    using function_type  = TReturn(TArgs...);
    using return_type    = TReturn;
    using object_type    = void;
    using argument_types = etl::type_list<TArgs...>;
 
    static constexpr bool   is_function        = true;
    static constexpr bool   is_member_function = false;
    static constexpr bool   is_functor         = false;
    static constexpr bool   is_const           = false;
    static constexpr bool   is_volatile        = false;
    static constexpr bool   is_noexcept        = false;
    static constexpr size_t arity              = sizeof...(TArgs);
    
    ETL_DEPRECATED_REASON("Use etl::function_traits::arity instead")
    static constexpr size_t argument_count     = arity;
  };
 
  //***************************************************************************
  // Free function pointer
  //***************************************************************************
  template <typename TReturn, typename... TArgs>
  struct function_traits<TReturn(*)(TArgs...), void> : function_traits<TReturn(TArgs...)> {};
 
  //***************************************************************************
  // Free function reference
  //***************************************************************************
  template <typename TReturn, typename... TArgs>
  struct function_traits<TReturn(&)(TArgs...), void> : function_traits<TReturn(TArgs...)> {};
 
#if ETL_HAS_NOEXCEPT_FUNCTION_TYPE
  //***************************************************************************
  // Free noexcept function pointer
  //***************************************************************************
  template <typename TReturn, typename... TArgs>
  struct function_traits<TReturn(*)(TArgs...) noexcept, void> : function_traits<TReturn(TArgs...)>
  {
    static constexpr bool is_noexcept = true;
  };
 
  //***************************************************************************
  // Free noexcept function reference.
  //***************************************************************************
  template <typename TReturn, typename... TArgs>
  struct function_traits<TReturn(&)(TArgs...) noexcept, void> : function_traits<TReturn(TArgs...)>
  {
    static constexpr bool is_noexcept = true;
  };
#endif
 
  //***************************************************************************
  // Member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...), void> : function_traits<TReturn(TArgs...)>
  {
    using object_type = TObject;
    static constexpr bool is_function        = false;
    static constexpr bool is_member_function = true;
  };
 
  //***************************************************************************
  // Const member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) const, void> : function_traits<TReturn(TObject::*)(TArgs...)>
  {
    static constexpr bool is_const = true;
  };
 
  //***************************************************************************
  // Volatile member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) volatile, void> : function_traits<TReturn(TObject::*)(TArgs...)>
  {
    static constexpr bool is_volatile = true;
  };
 
  //***************************************************************************
  // Const volatile member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) const volatile, void> : function_traits<TReturn(TObject::*)(TArgs...)>
  {
    static constexpr bool is_const    = true;
    static constexpr bool is_volatile = true;
  };
 
#if ETL_HAS_NOEXCEPT_FUNCTION_TYPE
  //***************************************************************************
  // Noexcept member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) noexcept, void> : function_traits<TReturn(TObject::*)(TArgs...)>
  {
    static constexpr bool is_noexcept = true;
  };
 
  //***************************************************************************
  // Const noexcept member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) const noexcept, void> : function_traits<TReturn(TObject::*)(TArgs...) const>
  {
    static constexpr bool is_noexcept = true;
  };
 
  //***************************************************************************
  // Volatile noexcept member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) volatile noexcept, void> : function_traits<TReturn(TObject::*)(TArgs...) volatile>
  {
    static constexpr bool is_noexcept = true;
  };
 
  //***************************************************************************
  // Const volatile noexcept member function pointers
  //***************************************************************************
  template <typename TReturn, typename TObject, typename... TArgs>
  struct function_traits<TReturn (TObject::*)(TArgs...) const volatile noexcept, void> : function_traits<TReturn(TObject::*)(TArgs...) const volatile>
  {
    static constexpr bool is_noexcept = true;
  };
#endif
 
  //***************************************************************************
  // Forward cv/ref on the whole type to the unqualified type.
  //***************************************************************************
  template <typename T>
  struct function_traits<T, etl::enable_if_t<!etl::is_same<T, etl::remove_cvref_t<T>>::value &&
                                             !etl::is_class<etl::decay_t<T>>::value>>
    : function_traits<etl::remove_cvref_t<T>>
  {
  };
 
  //***************************************************************************
  // Functors / lambdas: enable only for class types that have a unique operator()
  //***************************************************************************
  namespace private_function_traits
  {
    //*********************************
    // Helper to get pointer to call operator
    //*********************************
    template <typename U>
    using call_operator_ptr_t = decltype(&U::operator());
  }
 
  //***************************************************************************
  //***************************************************************************
  template <typename T>
  struct function_traits<T, etl::enable_if_t<etl::is_class<etl::decay_t<T>>::value&&
                            etl::has_unique_call_operator<T>::value>>
    : function_traits<private_function_traits::call_operator_ptr_t<etl::decay_t<T>> >
  {
    static constexpr bool is_functor = true;
  };
 
  //***************************************************************************
  // Out-of-class definitions for the function_traits static members
  //***************************************************************************
  // free/function primary template
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(TArgs...), void>::is_function;
 
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(TArgs...), void>::is_member_function;
  
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(TArgs...), void>::is_functor;
  
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(TArgs...), void>::is_const;
  
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(TArgs...), void>::is_volatile;
  
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(TArgs...), void>::is_noexcept;
  
  template <typename TReturn, typename... TArgs>
  constexpr size_t function_traits<TReturn(TArgs...), void>::arity;
 
  // member-function-pointer specialization
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...), void>::is_function;
 
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...), void>::is_member_function;
 
  // cv/ref-qualified member-function pointer flags
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) const, void>::is_const;
  
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) volatile, void>::is_volatile;
  
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) const volatile, void>::is_const;
  
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) const volatile, void>::is_volatile;
 
#if ETL_HAS_NOEXCEPT_FUNCTION_TYPE
  template <typename TReturn, typename... TArgs>
  constexpr bool function_traits<TReturn(*)(TArgs...) noexcept, void>::is_noexcept;
 
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) noexcept, void>::is_noexcept;
 
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) const noexcept, void>::is_noexcept;
 
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) volatile noexcept, void>::is_noexcept;
 
  template <typename TReturn, typename TObject, typename... TArgs>
  constexpr bool function_traits<TReturn (TObject::*)(TArgs...) const volatile noexcept, void>::is_noexcept;
#endif
 
  //***************************************************************************
  // Functor / lambda specialisation: provide out-of-class definition for is_functor
  //***************************************************************************
  template <typename T>
  constexpr bool function_traits<T, etl::enable_if_t<etl::is_class<etl::decay_t<T>>::value &&
                                                     etl::has_unique_call_operator<T>::value>>::is_functor;
}
 
#endif
#endif