1++++++++++++++++++++++++++++++++++ 2 |Boost| Pointer Container Library 3++++++++++++++++++++++++++++++++++ 4 5.. |Boost| image:: boost.png 6 7Conventions 8+++++++++++ 9 10There are a few design decisions that will affect how the classes are 11used. Besides these the classes are much like normal standard containers 12and provides almost the same interface. The new conventions are: 13 14.. contents:: :local: 15 16Null pointers are not allowed by default 17---------------------------------------- 18 19If the user tries to insert the null pointer, the operation will throw a 20``bad_pointer`` exception (see `Example 1 <examples.html>`_). 21 22Use `nullable <reference.html#class-nullable>`_ to allow null pointers. 23 24Please notice that all preconditions of the form :: 25 26 x != 0; 27 28are not active when the you have instantiated a container 29with ``nullable<T>`` as in :: 30 31 boost::ptr_vector< boost::nullable<animal> > vec; 32 vec.push_back( 0 ); // ok 33 34All default iterators apply an extra layer of indirection 35--------------------------------------------------------- 36 37This is done to 38make the containers easier and safer to use. It promotes a kind of 39pointer-less programming and the user of a class needs not worry about 40pointers except when allocating them (see `Example 2 <examples.html>`_). Iterators that 41provide access to the naked pointers are also provided since they might be 42useful in rare cases. For example, whenever ``begin()`` returns an iterator, 43``ptr_begin()`` will return an iterator that allows one to iterate over the 44stored pointers. 45 46All comparison operations are done on the pointed to objects and not at the pointer level 47----------------------------------------------------------------------------------------- 48 49For example, in ``ptr_set<T>`` the ordering is by default done by 50``boost::ptr_less<T>`` which compares the indirected pointers. 51Similarly, ``operator==()`` for ``container<Foo>`` compares all objects 52with ``operator==(const Foo&, const Foo&)``. 53 54 55Stored elements are required to be `Cloneable <reference.html#the-Cloneable-concept>`_ for a subset of the operations 56--------------------------------------------------------------------------------------------------------------------- 57 58This is because most polymorphic objects cannot be copied directly, but 59they can often be so by a use of a member function (see `Example 4 <examples.html>`_). Often 60it does not even make sense to clone an object in which case a large 61subset of the operations are still workable. 62 63Whenever objects are inserted into a container, they are cloned before insertion 64-------------------------------------------------------------------------------- 65 66This is necessary because all pointer containers take ownerships of stored objects 67(see `Example 5 <examples.html>`_). 68 69Whenever pointers are inserted into a container, ownership is transferred to the container 70------------------------------------------------------------------------------------------ 71 72All containers take ownership of the stored pointers and therefore a 73container needs to have its own copies (see `Example 5 <examples.html>`_). 74 75Ownership can be transferred from a container on a per pointer basis 76-------------------------------------------------------------------- 77 78This 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 82Ownership can be transferred from a container to another container on a per iterator range basis 83------------------------------------------------------------------------------------------------ 84 85This makes it possible to exchange data safely between different pointer 86containers without cloning the objects again (see `Example 7 <examples.html>`_). 87 88A container can be cheaply returned from functions either by making a clone or by giving up ownership of the container 89---------------------------------------------------------------------------------------------------------------------- 90 91Two special member functions, ``clone()`` and ``release()``, both return a 92``compatible-smart-ptr<SmartContainer>`` which can be assigned to another pointer container. This 93effectively reduces the cost of returning a container to one 94heap-allocation plus a call to ``swap()`` (see `Example 3 <examples.html>`_). 95 96Iterators are invalidated as in the corresponding standard container 97-------------------------------------------------------------------- 98 99Because the containers in this library wrap standard containers, the 100rules for invalidation of iterators are the same as the rules 101of the corresponding standard container. 102 103For example, for both ``boost::ptr_vector<T>`` and ``std::vector<U>`` 104insertion and deletion only invalidates the deleted 105element and elements following it; all elements before the inserted/deleted 106element 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 124 125 126
