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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="typeof.tuto"></a>Tutorial</h2></div></div></div> |
| <p> |
| To start using typeof include the typeof header: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| To deduce the type of an expression at compile time use the <code class="computeroutput"><span class="identifier">BOOST_TYPEOF</span></code> |
| macro: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex1</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="number">1</span> <span class="special">+</span> <span class="number">0.5</span><span class="special">)</span> <span class="identifier">type</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">type</span><span class="special">,</span> <span class="keyword">double</span><span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| In the dependent context use <code class="computeroutput"><span class="identifier">BOOST_TYPEOF_TPL</span></code> |
| instead of <code class="computeroutput"><span class="identifier">BOOST_TYPEOF</span></code>: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex2</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> |
| <span class="identifier">BOOST_TYPEOF_TPL</span><span class="special">(</span><span class="identifier">T</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">U</span><span class="special">())</span> <span class="identifier">add</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">U</span><span class="special">&</span> <span class="identifier">u</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">t</span> <span class="special">+</span> <span class="identifier">u</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">add</span><span class="special">(</span><span class="char">'a'</span><span class="special">,</span> <span class="number">1.5</span><span class="special">))</span> <span class="identifier">type</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">type</span><span class="special">,</span> <span class="keyword">double</span><span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| The above examples are possible because the Typeof Library knows about primitive |
| types, such as <code class="computeroutput"><span class="keyword">int</span></code>, <code class="computeroutput"><span class="keyword">double</span></code>, <code class="computeroutput"><span class="keyword">char</span></code>, |
| etc. The Typeof Library also knows about most types and templates defined by |
| the Standard C++ Library, but the appropriate headers need to be included to |
| take advantage of this: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">/</span><span class="identifier">std</span><span class="special">/</span><span class="identifier">utility</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">ex3</span> |
| <span class="special">{</span> |
| <span class="identifier">BOOST_AUTO</span><span class="special">(</span><span class="identifier">p</span><span class="special">,</span> <span class="identifier">make_pair</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">));</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">p</span><span class="special">),</span> <span class="identifier">pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| Here <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">/</span><span class="identifier">std</span><span class="special">/</span><span class="identifier">utility</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> |
| includes <code class="computeroutput"><span class="special"><</span><span class="identifier">utility</span><span class="special">></span></code> and contains knowledge about templates |
| defined there. This naming convention applies in general, for example to let |
| the Typeof Library handle <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span></code>, |
| include <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">/</span><span class="identifier">std</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>, |
| etc. |
| </p> |
| <p> |
| To deduce the type of a variable from the expression, this variable is initialized |
| with, use the <code class="computeroutput"><span class="identifier">BOOST_AUTO</span></code> macro |
| (or <code class="computeroutput"><span class="identifier">BOOST_AUTO_TPL</span></code> in a dependent |
| context: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</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="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">ex4</span> |
| <span class="special">{</span> |
| <span class="identifier">BOOST_AUTO</span><span class="special">(</span><span class="identifier">p</span><span class="special">,</span> <span class="keyword">new</span> <span class="keyword">int</span><span class="special">[</span><span class="number">20</span><span class="special">]);</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">p</span><span class="special">),</span> <span class="keyword">int</span><span class="special">*>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| Both <code class="computeroutput"><span class="identifier">BOOST_TYPEOF</span></code> and <code class="computeroutput"><span class="identifier">BOOST_AUTO</span></code> strip top-level qualifiers. Therefore, |
| to allocate for example a reference, it has to be specified explicitly: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex5</span> |
| <span class="special">{</span> |
| <span class="identifier">string</span><span class="special">&</span> <span class="identifier">hello</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">static</span> <span class="identifier">string</span> <span class="identifier">s</span> <span class="special">=</span> <span class="string">"hello"</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">s</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">BOOST_AUTO</span><span class="special">(&</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">hello</span><span class="special">());</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| To better understand this syntax, note that this gets expanded into: |
| </p> |
| <pre class="programlisting"><span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">hello</span><span class="special">())</span> <span class="special">&</span><span class="identifier">s</span> <span class="special">=</span> <span class="identifier">hello</span><span class="special">();</span> |
| </pre> |
| <p> |
| If your define your own type, the Typeof Library cannot handle it unless you |
| let it know about this type. You tell the Typeof Library about a type (or template) |
| by the means of "registering" this type/template. |
| </p> |
| <p> |
| Any source or header file where types/templates are registered has to contain |
| the following line before any registration is done: |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="identifier">BOOST_TYPEOF_INCREMENT_REGISTRATION_GROUP</span><span class="special">()</span> |
| </pre> |
| <p> |
| After this a type can be registered: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex6</span> |
| <span class="special">{</span> |
| <span class="keyword">struct</span> <span class="identifier">MyType</span> |
| <span class="special">{};</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">BOOST_TYPEOF_REGISTER_TYPE</span><span class="special">(</span><span class="identifier">ex6</span><span class="special">::</span><span class="identifier">MyType</span><span class="special">)</span> |
| </pre> |
| <p> |
| The registration must be done from the context of global namespace; fully qualified |
| type name has to be used. |
| </p> |
| <p> |
| Any number of types can be registered in one file, each on a separate line. |
| </p> |
| <p> |
| Once your type is registered, the Typeof Library can handle it in any context: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex6</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">make_pair</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="identifier">MyType</span><span class="special">()))</span> <span class="identifier">type</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">MyType</span><span class="special">></span> <span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| A template is registered by specifying its fully qualified name, and describing |
| its parameters. In the simplest case, when all parameters are type parameters, |
| only their number needs to be specified: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex7</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">MyTemplate</span> |
| <span class="special">{};</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">BOOST_TYPEOF_REGISTER_TEMPLATE</span><span class="special">(</span><span class="identifier">ex7</span><span class="special">::</span><span class="identifier">MyTemplate</span><span class="special">,</span> <span class="number">2</span><span class="special">)</span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">ex7</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">make_pair</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="identifier">MyTemplate</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">ex6</span><span class="special">::</span><span class="identifier">MyType</span><span class="special">>()))</span> <span class="identifier">type</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="identifier">pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">MyTemplate</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">ex6</span><span class="special">::</span><span class="identifier">MyType</span><span class="special">></span> <span class="special">></span> |
| <span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| When a template has integral template parameters, all parameters need to be |
| described in the preprocessor sequence: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">ex8</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">n</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">MyTemplate</span> |
| <span class="special">{};</span> |
| <span class="special">}</span> |
| |
| <span class="identifier">BOOST_TYPEOF_REGISTER_TEMPLATE</span><span class="special">(</span><span class="identifier">ex8</span><span class="special">::</span><span class="identifier">MyTemplate</span><span class="special">,</span> <span class="special">(</span><span class="keyword">class</span><span class="special">)(</span><span class="keyword">int</span><span class="special">))</span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">ex8</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="identifier">make_pair</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="identifier">MyTemplate</span><span class="special"><</span><span class="identifier">ex7</span><span class="special">::</span><span class="identifier">MyTemplate</span><span class="special"><</span><span class="identifier">ex6</span><span class="special">::</span><span class="identifier">MyType</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>,</span> <span class="number">0</span><span class="special">>()))</span> <span class="identifier">type</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">((</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="identifier">pair</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">MyTemplate</span><span class="special"><</span><span class="identifier">ex7</span><span class="special">::</span><span class="identifier">MyTemplate</span><span class="special"><</span><span class="identifier">ex6</span><span class="special">::</span><span class="identifier">MyType</span><span class="special">,</span> <span class="keyword">int</span><span class="special">>,</span> <span class="number">0</span><span class="special">></span> <span class="special">></span> |
| <span class="special">>::</span><span class="identifier">value</span><span class="special">));</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| Please see the reference for more details. |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2004, 2005 Arkadiy Vertleyb, Peder Holt<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top"> |
| http://www.boost.org/LICENSE_1_0.txt </a>) |
| </p> |
| </div></td> |
| </tr></table> |
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