1++++++++++++++++++++++++++++++++++ 2 |Boost| Pointer Container Library 3++++++++++++++++++++++++++++++++++ 4 5.. |Boost| image:: boost.png 6 7================ 8Usage Guidelines 9================ 10 11.. contents:: :local: 12 13Choosing the right container 14---------------------------- 15 16The recommended usage pattern of the container classes is the same as 17for normal standard containers. 18 19``ptr_vector``, ``ptr_list`` and ``ptr_deque`` offer the programmer different 20complexity tradeoffs and should be used accordingly. ``ptr_vector`` is the 21type of sequence that should be used by default. ``ptr_list`` should be used 22when there are frequent insertions and deletions from the middle of the 23sequence and if the container is fairly large (eg. more than 100 24elements). ``ptr_deque`` is the data structure of choice when most insertions 25and deletions take place at the beginning or at the end of the sequence. 26The special container ``ptr_array`` may be used when the size of the container is invariant 27and known at compile time. 28 29An associative container supports unique keys if it may contain at most 30one element for each key. Otherwise, it supports equivalent keys. 31``ptr_set`` and ``ptr_map`` support unique keys. 32``ptr_multiset`` and ``ptr_multimap`` 33support equivalent keys. 34 35Recommended practice for Object-Oriented Programming 36---------------------------------------------------- 37 38Idiomatic Object-Oriented Programming in C++ looks a bit different from 39the way it is done in other languages. This is partly because C++ 40has both value and reference semantics, and partly because C++ is more flexible 41than other languages. Below is a list of recommendations that you are 42encouraged to follow: 43 441. Make base classes abstract and without data 45++++++++++++++++++++++++++++++++++++++++++++++ 46 47This has the following advantages: 48 49 a. It reduces *coupling* because you do not have to maintain or update state 50 51 .. 52 53 b. It helps you to avoid *slicing* 54 55 .. 56 57 c. It ensures you *override* the right function 58 59You might also want to read the following articles: 60 61- Kevlin Henney's `Six of the best`__ 62 63.. __: http://www.two-sdg.demon.co.uk/curbralan/papers/SixOfTheBest.pdf 64 65- Jack Reeves' `Multiple Inheritance Considered Useful`__ 66 67.. __: http://www.ddj.com/documents/s=10011/q=1/cuj0602reeves/0602reeves.html 68 69 702. Make virtual functions private and provide a non-virtual public forwarding function 71++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 72 73In code:: 74 75 class Polymorphic 76 { 77 private: 78 virtual int do_foo() = 0; 79 80 public: 81 int foo() 82 { 83 return do_foo(); 84 } 85 ... 86 }; 87 88This has the following advantages: 89 90 a. It makes sure all calls to the virtual function always goes through one place in your code 91 92 .. 93 94 b. It enables you to check preconditions and postconditions inside the forwarding function 95 96You might also want to read Herb Sutter's article `Virtuality`__. 97 98.. __: http://www.gotw.ca/publications/mill18.htm 99 1003. Derive your base class from ``boost::noncopyable`` 101+++++++++++++++++++++++++++++++++++++++++++++++++++++ 102 103Having an abstact base class prevents slicing when the base class is involved, but 104it does not prevent it for classes further down the hierarchy. This is where 105`boost::noncopyable`__ is handy to use:: 106 107 class Polymorphic : boost::noncopyable 108 { 109 ... 110 }; 111 112.. __ : http://www.boost.org/libs/utility/utility.htm#Class_noncopyable 113 114 1154. Avoid null-pointers in containers (if possible) 116++++++++++++++++++++++++++++++++++++++++++++++++++ 117 118By default the pointer containers do not allow you to store null-pointer in them. 119As you might know, this behavior can be changed explicitly with the use 120of `boost::nullable`__. 121 122The primary reason to avoid null-pointers 123is that you have to check for null-pointers every time the container is 124used. This extra checking is easy to forget, and it is somewhat contradictory to 125the spirit of OO where you replace special cases with dynamic dispatch. 126 127.. __: reference.html#class-nullable 128 129Often, however, you need to place some special object in the container because you 130do not have enough information to construct a full object. In that case 131you might be able to use the Null Object pattern which simply dictates that 132you implement virtual functions from the abstract base-class 133as empty functions or with dummy return values. This means that 134your OO-code still does not need to worry about null-pointers. 135 136You might want to read 137 138- Kevlin Henney's `Null Object - Something for Nothing`__ 139 140.. __: http://www.two-sdg.demon.co.uk/curbralan/papers/europlop/NullObject.pdf 141 142Finally you might end up in a situation where not even the Null Object can help 143you. That is when you truly need ``container< nullable<T> >``. 144 145.. raw:: html 146 147 <hr> 148 149**Navigate:** 150 151- `home <ptr_container.html>`_ 152- `reference <reference.html>`_ 153 154.. raw:: html 155 156 <hr> 157 158:Copyright: Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see LICENSE_1_0.txt__). 159 160__ http://www.boost.org/LICENSE_1_0.txt 161 162 163
