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typename [C++ Reference]
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<h2><a name="typename" id="typename">typename</a></h2>
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<h4><a name="specifying_type_parameters_to_templates" id="specifying_type_parameters_to_templates">Specifying Type Parameters To Templates</a></h4>
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In <a href="../keywords/template.html" class="wikilink1" title="keywords:template">template</a> argument lists <span class="curid"><a href="../keywords/typename.html" class="wikilink1" title="keywords:typename">typename</a></span> can be used interchangeably with <a href="../keywords/class.html" class="wikilink1" title="keywords:class">class</a> to indicate type parameters. Although there is no difference to the compiler, Alexandrescu recommends using <a href="../keywords/class.html" class="wikilink1" title="keywords:class">class</a> when the template argument is expected to be a <a href="../keywords/class.html" class="wikilink1" title="keywords:class">class</a> or <a href="../keywords/struct.html" class="wikilink1" title="keywords:struct">struct</a>, and <span class="curid"><a href="../keywords/typename.html" class="wikilink1" title="keywords:typename">typename</a></span> for other classes of types. This is purely to encourage source readability.
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<h4><a name="disambiguating_dependent_names" id="disambiguating_dependent_names">Disambiguating Dependent Names</a></h4>
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The <span class="curid"><a href="../keywords/typename.html" class="wikilink1" title="keywords:typename">typename</a></span> keyword is also used to indicate that a <a href="../keywords/dependent_name.html" class="wikilink1" title="keywords:dependent_name">dependent name</a> in a template definition refers to a type.
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<pre class="c code c++" style="font-family:monospace;"><span class="kw4">struct</span> Foo <span class="br0">{</span>
<span class="kw4">typedef</span> <span class="kw4">int</span> Type<span class="sy0">;</span>
<span class="br0">}</span><span class="sy0">;</span>
template<span class="sy0"><</span>class T<span class="sy0">></span>
<span class="kw4">struct</span> Bar <span class="br0">{</span>
<span class="kw4">typedef</span> typename T<span class="sy0">::</span><span class="me2">Type</span> BarType<span class="sy0">;</span> <span class="co1">// In a typedef</span>
<span class="kw4">void</span> baz<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
typename T<span class="sy0">::</span><span class="me2">Type</span> instance<span class="sy0">;</span> <span class="co1">// In a declaration</span>
<span class="br0">}</span>
<span class="br0">}</span><span class="sy0">;</span>
<span class="kw4">typedef</span> Bar<span class="sy0"><</span>Foo<span class="sy0">></span> FooBar<span class="sy0">;</span></pre>
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Related Topics: <a href="../keywords/class.html" class="wikilink1" title="keywords:class">class</a>, <a href="../keywords/template.html" class="wikilink1" title="keywords:template">template</a>
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