ceph/src/boost/libs/mpl/doc/src/refmanual/size.rst

   1 .. Sequences/Intrinsic Metafunctions//size
   2
   3 size
   4 ====
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Sequence
  13         >
  14     struct size
  15     {
  16         typedef |unspecified| type;
  17     };
  18
  19
  20
  21 Description
  22 -----------
  23
  24 ``size`` returns the number of elements in the sequence, that is, the number of elements
  25 in the range [``begin<Sequence>::type``, ``end<Sequence>::type``).
  26
  27
  28 Header
  29 ------
  30
  31 .. parsed-literal::
  32
  33     #include <boost/mpl/size.hpp>
  34
  35
  36
  37 Model of
  38 --------
  39
  40 |Tag Dispatched Metafunction|
  41
  42
  43 Parameters
  44 ----------
  45
  46 +---------------+-----------------------+-----------------------------------------------+
  47 | Parameter     | Requirement           | Description                                   |
  48 +===============+=======================+===============================================+
  49 | ``Sequence``  | |Forward Sequence|    | A sequence to query.                          |
  50 +---------------+-----------------------+-----------------------------------------------+
  51
  52
  53 Expression semantics
  54 --------------------
  55
  56
  57 For any |Forward Sequence| ``s``:
  58
  59
  60 .. parsed-literal::
  61
  62     typedef size<s>::type n;
  63
  64 :Return type:
  65     |Integral Constant|.
  66
  67 :Semantics:
  68     Equivalent to
  69
  70     .. parsed-literal::
  71
  72        typedef distance< begin<s>::type,end<s>::type >::type n;
  73
  74
  75 :Postcondition:
  76     ``n::value >= 0``.
  77
  78
  79
  80 Complexity
  81 ----------
  82
  83 The complexity of the ``size`` metafunction directly depends on the implementation of
  84 the particular sequence it is applied to. In the worst case, ``size`` guarantees a
  85 linear complexity.
  86
  87 If the ``s`` is a |Random Access Sequence|, ``size<s>::type`` is an |O(1)| operation.
  88 The opposite is not necessarily true |--| for example, a sequence class that models
  89 |Forward Sequence| might still give us an |O(1)| ``size`` implementation.
  90
  91
  92 Example
  93 -------
  94
  95 .. parsed-literal::
  96
  97     typedef list0<> empty_list;
  98     typedef vector_c<int,0,1,2,3,4,5> numbers;
  99     typedef range_c<int,0,100> more_numbers;
 100
 101     BOOST_MPL_ASSERT_RELATION( size<list>::value, ==, 0 );
 102     BOOST_MPL_ASSERT_RELATION( size<numbers>::value, ==, 5 );
 103     BOOST_MPL_ASSERT_RELATION( size<more_numbers>::value, ==, 100 );
 104
 105
 106 See also
 107 --------
 108
 109 |Forward Sequence|, |Random Access Sequence|, |empty|, |begin|, |end|, |distance|
 110
 111
 112 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 113    Distributed under the Boost Software License, Version 1.0. (See accompanying
 114    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)