[ceph.git] / ceph / src / boost / libs / metaparse / doc / nullary_metafunction.qbk

[#nullary_metafunction]
[section Nullary template metafunction]

A ['nullary template metafuncion] is a [link metafunction template metafunction]
taking 0 arguments. It is a type with a nested type called `type`, which is the
return value of the nullary metafunction. For example:

  struct always13
  {
    using type = std::integral_constant<int, 13>;
  };

This metafunction is called `always13`. It is a nullary metafunction, because it
takes no arguments. It always returns `std::integral_constant<int, 13>`.

To call this metafunction, one has to access its `::type`. For example:

  always13::type

The above example calls the metafunction to get
`std::integral_constant<int, 13>`.

[endsect]
Commit	Line	Data
7c673cae FG	1	[#nullary_metafunction]
	2	[section Nullary template metafunction]
	3
	4	A ['nullary template metafuncion] is a [link metafunction template metafunction]
	5	taking 0 arguments. It is a type with a nested type called `type`, which is the
	6	return value of the nullary metafunction. For example:
	7
	8	struct always13
	9	{
	10	using type = std::integral_constant<int, 13>;
	11	};
	12
	13	This metafunction is called `always13`. It is a nullary metafunction, because it
	14	takes no arguments. It always returns `std::integral_constant<int, 13>`.
	15
	16	To call this metafunction, one has to access its `::type`. For example:
	17
	18	always13::type
	19
	20	The above example calls the metafunction to get
	21	`std::integral_constant<int, 13>`.
	22
	23	[endsect]
	24