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POHow to use a template parameter in another template parameter declared before
 

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    <p>a template parameter can be used in another template parameter that follows it this way :</p> <pre><code>template&lt;typename T, T N&gt; struct s { }; </code></pre> <p>But is it possible to reference "T" if it is declared after "N" ?</p> <p>This does not work :</p> <pre><code>template&lt;T N, typename T&gt; struct s { }; </code></pre> <p>Can we help the compiler by pre-declaring "T" or doing anything else ?</p> <p>Thanks by advance.</p> <p>EDIT : as the first two replies were asking "why are you willing to do that ?" I'll explain the goal :</p> <p>I would like to make the compiler infer the type "T" in order to make the use of templated classes easier.</p> <p>For example :</p> <pre><code>template&lt;typename T, T A, T B&gt; struct sum { static T const value = A + B; }; </code></pre> <p>This template can be used this way :</p> <pre><code>sum&lt;int, 1, 2&gt;::value </code></pre> <p>But it would be better if it could be used this way :</p> <pre><code>sum&lt;1, 2&gt;::value </code></pre> <p>Technically it's should be possible because the compiler knows the types of "1" and "2" : "int", and in fact it uses these informations to find the best overload for a function. So by declaring the template this way :</p> <pre><code>template&lt;T A, T B, typename T&gt; struct sum { static T const value = A + B; }; </code></pre> <p>the compiler could use its capability to infer the last parameter from the informations provided by the first and the second one, and then find the best template to instantiate.</p>
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