function_traits

template <class F>
struct function_traits
{
   static const std::size_t    arity = see-below;
   typedef see-below           result_type;
   typedef see-below           argN_type;
};

The class template function_traits will only compile if:

The compiler supports partial specialization of class templates.
The template argument F is a function type, note that this is not the same thing as a pointer to a function.

	Tip
	function_traits is intended to introspect only C++ functions of the form R (), R( A1 ), R ( A1, ... etc. ) and not function pointers or class member functions. To convert a function pointer type to a suitable type use remove_pointer.

Table 1.20. Function Traits Members

Member	Description
`function_traits<F>::arity`	An integral constant expression that gives the number of arguments accepted by the function type `F`.
`function_traits<F>::result_type`	The type returned by function type `F`.
`function_traits<F>::argN_type`	The `N`th argument type of function type `F`, where `1 <= N <= arity` of `F`.

Table 1.21. Examples

Expression	Result
`function_traits<void (void)>::arity`	An integral constant expression that has the value 0.
`function_traits<long (int)>::arity`	An integral constant expression that has the value 1.
`function_traits<long (int, long, double, void*)>::arity`	An integral constant expression that has the value 4.
`function_traits<void (void)>::result_type`	The type `void`.
`function_traits<long (int)>::result_type`	The type `long`.
`function_traits<long (int)>::arg1_type`	The type `int`.
`function_traits<long (int, long, double, void*)>::arg4_type`	The type `void*`.
`function_traits<long (int, long, double, void*)>::arg5_type`	A compiler error: there is no `arg5_type` since there are only four arguments.
`function_traits<long (*)(void)>::arity`	A compiler error: argument type is a function pointer, and not a function type.

Compiler Compatibility: All current compilers are supported by this trait.

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function_traits