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PO"could not convert template argument" to its own type
 

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  1. PO"could not convert template argument" to its own type
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    <p>I'm trying to make a type which can type-safely encapsulate arbitrary types. I got the idea in my head that this might be possible from this answer: <a href="https://stackoverflow.com/questions/4298408/5-years-later-is-there-something-better-than-the-fastest-possible-c-delegate/4300544#4300544">5 years later, is there something better than the &quot;Fastest Possible C++ Delegates&quot;?</a> So far I have only succeeded in moving the problem, but I ran into an error that I can't find the root of.</p> <p>The compiler seems to be telling me that it can't cast the value to the value's own type, which strikes me as bizarre.</p> <p>I am running Mac OS X 10.6 with llvm-gcc 4.2 (gcc 4.2.1 front-end).</p> <p>Suggestions of how to get rid of the void* or move it to a less consequential position are welcome, but this question isn't really about that.</p> <p>The error:</p> <pre><code>$ g++ main.cpp main.cpp: In static member function ‘static Stamp StampFactory&lt;T&gt;::make(T*) [with T = int]’: main.cpp:33: instantiated from ‘Stamp makeStamp(T*) [with T = int]’ main.cpp:39: instantiated from here main.cpp:26: error: could not convert template argument ‘t’ to ‘int*’ </code></pre> <p>The code:</p> <pre><code>typedef void (*VoidFunc)(void*); struct Stamp { Stamp(VoidFunc p) { this-&gt;press = p; } VoidFunc press; }; template&lt;typename T&gt; struct StampFactory { template&lt;T* rvalue&gt; struct Pattern { void operator()(void* lvalue) { *dynamic_cast&lt;T*&gt;(lvalue) = *rvalue; } }; static Stamp make(T* t) { return Stamp(Pattern&lt;t&gt;()); // 28 } }; template&lt;typename T&gt; Stamp makeStamp(T* t) { return StampFactory&lt;T&gt;::make(t); // 33 } int main(int argc, char** argv) { int i = 0; Stamp s = makeStamp(&amp;i); //39 } </code></pre>
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    1. COThis might be stupid but shouldn't Pattern<t> be Pattern<T> seeing as t is the function parameter's name?
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    2. CO@Borgleader: Looking at the declaration of Pattern, I think it is not a typo.
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      1. USMikael Persson
    3. CO@Borgleader I'm passing t as a non-type template argument of type T*. That part is right, but it's not very easy to understand; I've spent several hours wrapping my head around what the answerer of the other question did for a similar effect.
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