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1 | <section id="array.intro"> |
2 | <title>Introduction</title> | |
3 | ||
4 | <using-namespace name="boost"/> | |
5 | <using-class name="array"/> | |
6 | ||
7 | <para>The C++ Standard Template Library STL as part of the C++ | |
8 | Standard Library provides a framework for processing algorithms on | |
9 | different kind of containers. However, ordinary arrays don't | |
10 | provide the interface of STL containers (although, they provide | |
11 | the iterator interface of STL containers).</para> | |
12 | ||
13 | <para>As replacement for ordinary arrays, the STL provides class | |
14 | <code><classname>std::vector</classname></code>. However, | |
15 | <code><classname>std::vector<></classname></code> provides | |
16 | the semantics of dynamic arrays. Thus, it manages data to be able | |
17 | to change the number of elements. This results in some overhead in | |
18 | case only arrays with static size are needed.</para> | |
19 | ||
20 | <para>In his book, <emphasis>Generic Programming and the | |
21 | STL</emphasis>, Matthew H. Austern introduces a useful wrapper | |
22 | class for ordinary arrays with static size, called | |
23 | <code>block</code>. It is safer and has no worse performance than | |
24 | ordinary arrays. In <emphasis>The C++ Programming | |
25 | Language</emphasis>, 3rd edition, Bjarne Stroustrup introduces a | |
26 | similar class, called <code>c_array</code>, which I (<ulink | |
27 | url="http://www.josuttis.com">Nicolai Josuttis</ulink>) present | |
28 | slightly modified in my book <emphasis>The C++ Standard Library - | |
29 | A Tutorial and Reference</emphasis>, called | |
30 | <code>carray</code>. This is the essence of these approaches | |
31 | spiced with many feedback from <ulink | |
32 | url="http://www.boost.org">boost</ulink>.</para> | |
33 | ||
34 | <para>After considering different names, we decided to name this | |
35 | class simply <code><classname>array</classname></code>.</para> | |
36 | ||
37 | <para>Note that this class is suggested to be part of the next | |
38 | Technical Report, which will extend the C++ Standard (see | |
39 | <ulink url="http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm">http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</ulink>).</para> | |
40 | ||
41 | <para>Class <code><classname>array</classname></code> fulfills most | |
42 | but not all of the requirements of "reversible containers" (see | |
43 | Section 23.1, [lib.container.requirements] of the C++ | |
44 | Standard). The reasons array is not an reversible STL container is | |
45 | because: | |
46 | <itemizedlist spacing="compact"> | |
47 | <listitem><simpara>No constructors are provided.</simpara></listitem> | |
48 | <listitem><simpara>Elements may have an undetermined initial value (see <xref linkend="array.rationale"/>).</simpara></listitem> | |
49 | <listitem><simpara><functionname>swap</functionname>() has no constant complexity.</simpara></listitem> | |
50 | <listitem><simpara><methodname>size</methodname>() is always constant, based on the second template argument of the type.</simpara></listitem> | |
51 | <listitem><simpara>The container provides no allocator support.</simpara></listitem> | |
52 | </itemizedlist> | |
53 | </para> | |
54 | ||
55 | <para>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that: | |
56 | <itemizedlist spacing="compact"> | |
57 | <listitem><simpara><methodname>front</methodname>() and <methodname>back</methodname>() are provided.</simpara></listitem> | |
58 | <listitem><simpara><methodname>operator[]</methodname> and <methodname>at</methodname>() are provided.</simpara></listitem> | |
59 | </itemizedlist> | |
60 | </para> | |
61 | </section> | |
62 | ||
63 | ||
64 |