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15      <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Tuples</b></font>
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28<p>
29Tuples are the most basic infrastructure that the framework builds with. This sub-library provides a mechanism to bundle objects of arbitrary types in a single structure. Tuples hold heterogeneous types up to a predefined maximum.</p>
30<p>
31Only the most basic functionality needed are provided. This is a straight-forward and extremely lean and mean library. Unlike other recursive list-like tuple implementations, this tuple library implementation uses simple structs similar to std::pair with specialization for 0 to N tuple elements, where N is a predefined constant. There are only 4 tuple operations to learn:</p>
32<p>
331)  Construction</p>
34<p>
35Here are examples on how to construct tuples:</p>
36<code><pre>
37    <span class=keyword>typedef </span><span class=identifier>tuple</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>, </span><span class=keyword>char</span><span class=special>&gt; </span><span class=identifier>t1_t</span><span class=special>;
38    </span><span class=keyword>typedef </span><span class=identifier>tuple</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>, </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>, </span><span class=keyword>double</span><span class=special>&gt; </span><span class=identifier>t2_t</span><span class=special>;
39
40    //  </span><span class=keyword>this </span><span class=identifier>tuple </span><span class=identifier>has </span><span class=identifier>an </span><span class=keyword>int </span><span class=keyword>and </span><span class=keyword>char </span><span class=identifier>members
41    </span><span class=identifier>t1_t </span><span class=identifier>t1</span><span class=special>(</span><span class=number>3</span><span class=special>, </span><span class=literal>'c'</span><span class=special>);
42
43    //  </span><span class=keyword>this </span><span class=identifier>tuple </span><span class=identifier>has </span><span class=identifier>an </span><span class=keyword>int</span><span class=special>, </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=keyword>and </span><span class=keyword>double </span><span class=identifier>members
44    </span><span class=identifier>t2_t </span><span class=identifier>t2</span><span class=special>(</span><span class=number>3</span><span class=special>, </span><span class=string>&quot;hello&quot;</span><span class=special>, </span><span class=number>3.14</span><span class=special>);
45</span></pre></code>
46<p>
472)  Member access</p>
48<p>
49A member in a tuple can be accessed using the tuple's  operator by specifying the Nth tuple_index. Here are some examples:</p>
50<code><pre>
51    <span class=identifier>tuple_index</span><span class=special>&lt;</span><span class=number>0</span><span class=special>&gt; </span><span class=identifier>ix0</span><span class=special>; // </span><span class=number>0</span><span class=identifier>th </span><span class=identifier>index </span><span class=special>== </span><span class=number>1</span><span class=identifier>st </span><span class=identifier>item
52    </span><span class=identifier>tuple_index</span><span class=special>&lt;</span><span class=number>1</span><span class=special>&gt; </span><span class=identifier>ix1</span><span class=special>; // </span><span class=number>1</span><span class=identifier>st </span><span class=identifier>index </span><span class=special>== </span><span class=number>2</span><span class=identifier>nd </span><span class=identifier>item
53    </span><span class=identifier>tuple_index</span><span class=special>&lt;</span><span class=number>2</span><span class=special>&gt; </span><span class=identifier>ix2</span><span class=special>; // </span><span class=number>2</span><span class=identifier>nd </span><span class=identifier>index </span><span class=special>== </span><span class=number>3</span><span class=identifier>rd </span><span class=identifier>item
54
55    </span><span class=comment>//  Note zero based indexing. 0 = 1st item, 1 = 2nd item
56
57    </span><span class=identifier>t1</span><span class=special>[</span><span class=identifier>ix0</span><span class=special>] = </span><span class=number>33</span><span class=special>;       // </span><span class=identifier>sets </span><span class=identifier>the </span><span class=keyword>int </span><span class=identifier>member </span><span class=identifier>of </span><span class=identifier>the </span><span class=identifier>tuple </span><span class=identifier>t1
58    </span><span class=identifier>t2</span><span class=special>[</span><span class=identifier>ix2</span><span class=special>] = </span><span class=number>6e6</span><span class=special>;      // </span><span class=identifier>sets </span><span class=identifier>the </span><span class=keyword>double </span><span class=identifier>member </span><span class=identifier>of </span><span class=identifier>the </span><span class=identifier>tuple </span><span class=identifier>t2
59    </span><span class=identifier>t1</span><span class=special>[</span><span class=identifier>ix1</span><span class=special>] = </span><span class=literal>'a'</span><span class=special>;      // </span><span class=identifier>sets </span><span class=identifier>the </span><span class=keyword>char </span><span class=identifier>member </span><span class=identifier>of </span><span class=identifier>the </span><span class=identifier>tuple </span><span class=identifier>t1
60</span></pre></code>
61<p>
62Access to out of bound indexes returns a nil_t value.</p>
63<p>
643)  Member type inquiry</p>
65<p>
66The type of an individual member can be queried. Example:</p>
67<code><pre>
68    <span class=identifier>tuple_element</span><span class=special>&lt;</span><span class=number>1</span><span class=special>, </span><span class=identifier>t2_t</span><span class=special>&gt;::</span><span class=identifier>type
69</span></pre></code>
70<p>
71Refers to the type of the second member (again note zero based indexing, hence 0 = 1st item, 1 = 2nd item) of the tuple.</p>
72<p>
73Access to out of bound indexes returns a nil_t type.</p>
74<p>
754)  Tuple length</p>
76<p>
77The number of elements in a tuple can be queried. Example:</p>
78<code><pre>
79    <span class=keyword>int </span><span class=identifier>n </span><span class=special>= </span><span class=identifier>t1</span><span class=special>.</span><span class=identifier>length</span><span class=special>;
80</span></pre></code>
81<p>
82gets the number of elements in tuple t1.</p>
83<p>
84length is a static constant. Thus, TupleT::length also works. Example:</p>
85<code><pre>
86    <span class=keyword>int </span><span class=identifier>n </span><span class=special>= </span><span class=identifier>t1_t</span><span class=special>::</span><span class=identifier>length</span><span class=special>;
87</span></pre></code>
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97<p class="copyright">Copyright &copy; 2001-2002 Joel de Guzman<br>
98  <br>
99<font size="2">Use, modification and distribution is subject to the Boost Software
100    License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
101    http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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