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POWhy this statement does not call the constructors - C++
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  1. POWhy this statement does not call the constructors - C++
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    copied!<p>A template class and a normal class:</p> <pre><code>template &lt;typename Type&gt; class Holder { public: Holder(const Type&amp; value) : held_(value) { cout &lt;&lt; "Holder(const Type&amp; value)" &lt;&lt; endl; } Type&amp; Ref() { return held_; } private: Type held_; }; class Animal { public: Animal(const Animal&amp; rhs) { cout &lt;&lt; "Animal(const Animal&amp; rhs)" &lt;&lt; endl; } Animal() { cout &lt;&lt; "Animal()" &lt;&lt; endl; } ~Animal() { cout &lt;&lt; "~Animal" &lt;&lt; endl; } void Print() const { cout &lt;&lt; "Animal::Print()" &lt;&lt; endl; } }; </code></pre> <p>Then I want to instantiate a <code>Holder&lt;Animal&gt;</code> with this statement <code>Holder&lt;Animal&gt; a(Animal());</code>, however, it fails. I mean <code>Animal()</code> is not treated as a temporary object. And this statement doesn't call <code>Holder</code>'s constructor.</p> <p>If someone could explain? I'm not clear. I'm guessing <code>a</code> becomes a type here. Then, I use <code>Holder&lt;Animal&gt; a = Holder&lt;Animal&gt;(Animal());</code>, it works well. So, there are some cases here:</p> <ol> <li><code>Holder&lt;Animal&gt; a(Animal()); a.Ref().Print(); // error</code></li> <li><code>Holder&lt;Animal&gt; a = Holder&lt;Animal&gt;(Animal()); a.Ref().Print(); // ok</code></li> <li><code>Holder&lt;int&gt; b(4); b.Ref() = 10; cout &lt;&lt; b.Ref() &lt;&lt; endl; //ok</code></li> </ol> <p>Can explain? I'm just a little confused with the first statement. And the error information this statement causes:</p> <p><code>GCC4.7.2</code>: <code>error: request for member 'Ref' in 'a', which is of non-class type 'Holder&lt;Animal&gt;(Animal (*)())'</code></p> <p><code>VS10</code>: <code>error C2228: left of '.Ref' must have class/struct/union</code>, <code>error C2228: left of '.Print' must have class/struct/union</code></p>
 

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