ceph/src/boost/libs/ptr_container/doc/conventions.rst

   1 ++++++++++++++++++++++++++++++++++
   2  |Boost| Pointer Container Library
   3 ++++++++++++++++++++++++++++++++++
   4
   5 .. |Boost| image:: boost.png
   6
   7 Conventions
   8 +++++++++++
   9
  10 There are a few design decisions that will affect how the classes are
  11 used.  Besides these the classes are much like normal standard containers
  12 and provides almost the same interface.  The new conventions are:
  13
  14 .. contents:: :local:
  15
  16 Null pointers are not allowed by default
  17 ----------------------------------------
  18
  19 If the user tries to insert the null pointer, the operation will throw a
  20 ``bad_pointer`` exception (see `Example 1 <examples.html>`_).
  21
  22 Use `nullable <reference.html#class-nullable>`_ to allow null pointers.
  23
  24 Please notice that all preconditions of the form ::
  25
  26     x != 0;
  27
  28 are not active when the you have instantiated a container
  29 with ``nullable<T>`` as in ::
  30
  31     boost::ptr_vector< boost::nullable<animal> > vec;
  32     vec.push_back( 0 ); // ok
  33
  34 All default iterators apply an extra layer of indirection
  35 ---------------------------------------------------------
  36
  37 This is done to
  38 make the containers easier and safer to use.  It promotes a kind of
  39 pointer-less programming and the user of a class needs not worry about
  40 pointers except when allocating them (see `Example 2 <examples.html>`_).  Iterators that
  41 provide access to the naked pointers are also provided since they might be
  42 useful in rare cases. For example, whenever ``begin()`` returns an iterator,
  43 ``ptr_begin()`` will return an iterator that allows one to iterate over the
  44 stored pointers.
  45
  46 All comparison operations are done on the pointed to objects and not at the pointer level
  47 -----------------------------------------------------------------------------------------
  48
  49 For example, in ``ptr_set<T>`` the ordering is by default done by
  50 ``boost::ptr_less<T>`` which compares the indirected pointers.
  51 Similarly, ``operator==()`` for ``container<Foo>`` compares all objects
  52 with ``operator==(const Foo&, const Foo&)``.
  53
  54
  55 Stored elements are required to be `Cloneable <reference.html#the-Cloneable-concept>`_ for a subset of the operations
  56 ---------------------------------------------------------------------------------------------------------------------
  57
  58 This is because most polymorphic objects cannot be copied directly, but
  59 they can often be so by a use of a member function (see `Example 4 <examples.html>`_).  Often
  60 it does not even make sense to clone an object in which case a large
  61 subset of the operations are still workable.
  62
  63 Whenever objects are inserted into a container, they are cloned before insertion
  64 --------------------------------------------------------------------------------
  65
  66 This is necessary because all pointer containers take ownerships of stored objects
  67 (see `Example 5 <examples.html>`_).
  68
  69 Whenever pointers are inserted into a container, ownership is transferred to the container
  70 ------------------------------------------------------------------------------------------
  71
  72 All containers take ownership of the stored pointers and therefore a
  73 container needs to have its own copies (see `Example 5 <examples.html>`_).
  74
  75 Ownership can be transferred from a container on a per pointer basis
  76 --------------------------------------------------------------------
  77
  78 This can of course also be convenient.  Whenever it happens, an
  79 ``SmartContainer::auto_type`` object is used to provide an exception-safe transfer
  80 (see `Example 6 <examples.html>`_).
  81
  82 Ownership can be transferred from a container to another container on a per iterator range basis
  83 ------------------------------------------------------------------------------------------------
  84
  85 This makes it possible to exchange data safely between different pointer
  86 containers without cloning the objects again (see `Example 7 <examples.html>`_).
  87
  88 A container can be cheaply returned from functions either by making a clone or by giving up ownership of the container
  89 ----------------------------------------------------------------------------------------------------------------------
  90
  91 Two special member functions, ``clone()`` and ``release()``, both return an
  92 ``auto_ptr<SmartContainer>`` which can be assigned to another pointer container.  This
  93 effectively reduces the cost of returning a container to one
  94 heap-allocation plus a call to ``swap()`` (see `Example 3 <examples.html>`_).
  95
  96 Iterators are invalidated as in the corresponding standard container
  97 --------------------------------------------------------------------
  98
  99 Because the containers in this library wrap standard containers, the
 100 rules for invalidation of iterators are the same as the rules
 101 of the corresponding standard container.
 102
 103 For example, for both ``boost::ptr_vector<T>`` and ``std::vector<U>``
 104 insertion and deletion only invalidates the deleted
 105 element and elements following it; all elements before the inserted/deleted
 106 element remain valid.
 107
 108 .. raw:: html
 109
 110         <hr>
 111
 112 **Navigate:**
 113
 114 - `home <ptr_container.html>`_
 115 - `reference <reference.html>`_
 116
 117 .. raw:: html
 118
 119         <hr>
 120
 121 :Copyright:     Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see LICENSE_1_0.txt__).
 122
 123 __ http://www.boost.org/LICENSE_1_0.txt
 124
 125