reference.rst

C++的一个好库。。。现在很流行

  :Returns: a “singleton instance”: the same object will be
    returned on each invocation of ``get()``.

  :Thread Safety: ``get()`` can be called from multiple threads
    simultaneously.

``parameters``
--------------

Provides an interface for assembling the actual arguments to a
`forwarding function` into an |ArgumentPack|, in which any
|positional| arguments will be tagged according to the
corresponding template argument to ``parameters``.  

.. _forwarding function: `forwarding functions`_

:Defined in: `boost/parameter/parameters.hpp`__

__ ../../../../boost/parameter/parameters.hpp

.. parsed-literal::

    template <class P0 = *unspecified*, class P1 = *unspecified*, …class P\ β = *unspecified*>
    struct parameters
    {
        template <class A0, class A1 = *unspecified*, …class A\ β = *unspecified*>
        struct `match`_
        {
            typedef … type;
        };

        template <class A0>
        |ArgumentPack|_ `operator()`_\(A0 const& a0) const;

        template <class A0, class A1>
        |ArgumentPack|_ `operator()`_\(A0 const& a0, A1 const& a1) const; :vellipsis:`\ 
       .
       .
       .
     `
        template <class A0, class A1, …class A\ β>
        |ArgumentPack|_ `operator()`_\(A0 const& a0, A1 const& a1, …A\ β const& a\ β) const;
    };


:Requires: ``P0``, ``P1``, … ``P``\ β are models of |ParameterSpec|_. 


.. Note::

  In this section, ``R``\ *i* and ``K``\ *i* are defined as
  follows, for any argument type ``A``\ *i*:


     | ``R``\ *i* is ``A``\ *i*\ 's |intended argument type|
     |
     |  if ``A``\ *i* is a result type of ``keyword<T>::``\ |operator=|_
     |  then 
     |      ``K``\ *i* is ``T``
     |  else 
     |      ``K``\ *i* is ``P``\ *i*\ 's |keyword tag type|.


.. _match:

``match``
  A |Metafunction|_ used to remove a `forwarding function`_ from overload resolution.

  :Returns: if ``P0``, ``P1``, …\ ``P``\ β are *satisfied* (see
    below), then ``parameters<P0,P1,…Pβ>``.  Otherwise,
    ``match<A0,A1,…Aβ>::type`` is not defined.

  ``P0``, ``P1``, …\ ``P``\ β are **satisfied** if, for
  every *j* in 0…β, either:

  * ``P``\ *j* is the *unspecified* default
  * **or**, ``P``\ *j* is a specialization of |keyword|_,

  * **or**, ``P``\ *j* is |optional|_ ``<X,F>`` and either

    - ``X`` is not ``K``\ *i* for any *i*,
    - **or** ``X`` is some ``K``\ *i*  and ``mpl::apply<F,R``\ *i*\
      ``>::type::value`` is ``true``

  * **or**, ``P``\ *j* is |required|_ ``<X,F>``, and

    - ``X`` is some ``K``\ *i*, **and**
    - ``mpl::apply<F,R``\ *i*\ ``>::type::value`` is ``true``

.. _operator():

``operator()``
  .. parsed-literal::

      template <class A0> |ArgumentPack|_ operator()(A0 const& a0) const; :vellipsis:`\ 
        .
        .
        .
       `
      template <class A0, …class A\ β> |ArgumentPack|_ `operator()`_\(A0 const& a0, …A\ β const& a\ β) const;

  :Returns:
      An |ArgumentPack|_ containing, for each ``a``\ *i*,  

      - if ``a``\ *i*,  is a single-element |ArgumentPack|, its element
      - Otherwise, a |tagged reference| with |kw|_ ``K``\ *i* and *value* ``a``\ *i*


.. |optional| replace:: ``optional``
.. |required| replace:: ``required``

.. _optional:
.. _required:

``optional``, ``required``
--------------------------

These templates describe the requirements on a function parameter.

:Defined in: `boost/parameter/parameters.hpp`__

__ ../../../../boost/parameter/parameters.hpp

:Specializations model: |ParameterSpec|_

.. parsed-literal::

    template <class Tag, class Predicate = *unspecified*>
    struct optional;

    template <class Tag, class Predicate = *unspecified*>
    struct required;

The default value of ``Predicate`` is an unspecified |Metafunction|_ that returns
``mpl::true_`` for any argument.

.. |Metafunction| replace:: :concept:`Metafunction`
.. _Metafunction: ../../../mpl/doc/refmanual/metafunction.html

//////////////////////////////////////////////////////////////////////////////

Metafunctions
=============

A |Metafunction|_ is conceptually a function that operates on, and
returns, C++ types.

``binding``
-----------

Returns the result type of indexing an argument pack with a
|keyword tag type| or with a |tagged default|.

:Defined n: `boost/parameter/binding.hpp`__

__ ../../../../boost/parameter/binding.hpp

.. parsed-literal::

    template <class A, class K, class D = void>
    struct binding
    {
        typedef … type;
    };

:Requires: ``A`` is a model of |ArgumentPack|_.

:Returns: the reference type of the |tagged reference| in ``A``
  having |keyword tag type| ``K``, if any.  If no such |tagged
  reference| exists, returns ``D``.

``lazy_binding``
----------------

Returns the result type of indexing an argument pack with a |tagged
lazy default|.

:Defined in:
    `boost/parameter/binding.hpp`__

__ ../../../../boost/parameter/binding.hpp

.. parsed-literal::

    template <class A, class K, class F>
    struct lazy_binding
    {
        typedef … type;
    };

:Requires: ``A`` is a model of |ArgumentPack|_.

:Returns: the reference type of the |tagged reference| in ``A``
  having |keyword tag type| ``K``, if any.  If no such |tagged
  reference| exists, returns ``boost::``\ |result_of|_\ ``<F()>::type``. [#no_result_of]_


//////////////////////////////////////////////////////////////////////////////

Code Generation Macros
======================

Macros in this section can be used to ease the writing of code
using the Parameter libray by eliminating repetitive boilerplate.

``BOOST_PARAMETER_FUN(r,n,l,h,p)``
----------------------------------

Generates a sequence of `forwarding function`_ templates named
``n``, with arities ranging from ``l`` to ``h`` , returning ``r``,
and using ``p`` to control overload resolution and assign tags to
positional arguments.

:Defined in: `boost/parameter/macros.hpp`__

__ ../../../../boost/parameter/macros.hpp

:Requires: ``l`` and ``h`` are nonnegative integer tokens such
  that ``l`` < ``h``

Generates
  .. parsed-literal::

    template <class A1, class A2, …class A##\ **l**>
    r name(
        A1 const& a1, A2 const& a2, …A\ **l** const& x\ **l**
      , typename **p**::match<A1,A2,…A\ **l**>::type p = **p**\ ())
    {
       return **name**\ _with_named_params(**p**\ (x1,x2,…x\ **l**));
    }

    template <class A1, class A2, …class A\ **l**, class A\ ##\ BOOST_PP_INC_\ (**l**)>
    r name(
        A1 const& a1, A2 const& a2, …A\ **l** const& x\ **l**
      , A\ ##\ BOOST_PP_INC_\ (**l**) const& x\ ##\ BOOST_PP_INC_\ (**l**)
      , typename **p**::match<A1,A2,…A\ **l**,A\ ##\ BOOST_PP_INC_\ (**l**)>::type p = **p**\ ())
    {
       return **name**\ _with_named_params(**p**\ (x1,x2,…x\ **l**,x\ ##\ BOOST_PP_INC_\ (**l**)));
    } :vellipsis:`\ 
      .
      .
      .
     `
    template <class A1, class A2, …class A\ **h**>
    r name(
        A1 const& a1, A2 const& a2, …A\ **h** const& x\ **h**
      , typename **p**::match<A1,A2,…A\ **h**>::type p = **p**\ ())
    {
       return **name**\ _with_named_params(**p**\ (a1,a2,…a\ **h**));
    }


.. _BOOST_PP_INC: ../../../preprocessor/doc/ref/inc.html

``BOOST_PARAMETER_KEYWORD(n,k)``
--------------------------------

Generates the declaration of a |keyword tag type| named ``k`` in
namespace ``n``, and a corresponding |keyword object| definition in
the enclosing namespace.

:Defined in: `boost/parameter/keyword.hpp`__

__ ../../../../boost/parameter/keyword.hpp

Generates
  .. parsed-literal::

      namespace **n** { struct **k**; }
      namespace { 
        boost::parameter::keyword<*tag-namespace*::**k**>& **k**
        = boost::parameter::keyword<*tag-namespace*::**k**>::get();
      }

``BOOST_PARAMETER_MATCH(p,a,x)``
--------------------------------

Generates a defaulted parameter declaration for a `forwarding
function`_.

:Defined in: `boost/parameter/match.hpp`__

__ ../../../../boost/parameter/match.hpp

:Requires: ``a`` is a `Boost.Preprocessor sequence`__ 
  of the form 

  .. parsed-literal::

   (A0)(A1)…(A\ *n*)

__ http://www.boost.org/libs/preprocessor/doc/data.html

Generates
  .. parsed-literal::

    typename **p**::match<**A0**\ ,\ **A1**\ …,\ **A**\ *n*>::type **x** = **p**\ ()


Configuration Macros
====================

``BOOST_PARAMETER_MAX_ARITY``
-----------------------------

Determines the maximum number of arguments supported by the
library.  Will only be ``#defined`` by the library if it is not
already ``#defined``.

.. |BOOST_PARAMETER_MAX_ARITY| replace:: ``BOOST_PARAMETER_MAX_ARITY``

:Defined in: `boost/parameter/config.hpp`__

__ ../../../../boost/parameter/config.hpp

:Default Value: ``5``

Tutorial
========

Follow `this link`__ to the Boost.Parameter tutorial
documentation.  

__ index.html#tutorial

//////////////////////////////////////////////////////////////

.. [#thread] References to tag objects may be initialized multiple
   times.  This scenario can only occur in the presence of
   threading.  Because the C++ standard doesn't consider threading,
   it doesn't explicitly allow or forbid multiple initialization of
   references.  That said, it's hard to imagine an implementation
   where it could make a difference. 

.. [#no_result_of] Where |BOOST_NO_RESULT_OF|_ is ``#defined``,
   ``boost::``\ |result_of|_\ ``<F()>::type`` is replaced by
   ``F::result_type``.

.. |result_of| replace:: ``result_of``
.. _result_of: ../../../utility/utility.htm#result_of

.. |BOOST_NO_RESULT_OF| replace:: ``BOOST_NO_RESULT_OF``
.. _BOOST_NO_RESULT_OF: ../../../utility/utility.htm#BOOST_NO_RESULT_OF