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    <p>As mfontanini explains (and your compiler complains), non-type template parameters have to be compile-time constants. And your attempt to fool it by "const int p = i;" doesn't help; p may be constant variable, but it's not a compile-time constant. A C++11 compiler can do a better job telling you what's wrong here, but it can't help you get around the problem. In fact, there is no direct way around the problem.</p> <p>The simplest solution is an explicit switch, as user315052 suggests. And, if you're only doing this once, and just switching on 1 vs. 2, it's not worth putting in more effort than that.</p> <p>If you're doing the switch lots of times, of course, it's trivial to wrap it in a function:</p> <pre><code>void bar(int i) { switch(i) { case 1: foo(userInput&lt;1&gt;::typeName()); return; case 2: foo(userInput&lt;2&gt;::typeName()); return; default: throw someException; } </code></pre> <p>But if you have a lot more than 2 cases, or the set of values is in constant flux, you'll definitely want to use Boost.Preprocessor to automate the cruft, which would look something like this:</p> <pre><code>#define FOO_CASES_ 50 #define FOO_PASTE_(rep, i, _) case i: foo(userInput&lt; i &gt;::typeName()); return; void bar(int i) { switch (i) { BOOST_PP_REPEAT(FOO_CASES_, FOO_PASTE_, _) default: throw someException; } } #undef FOO_CASES_ #undef FOO_PASTE_ </code></pre> <p>Or, alternatively, write a code generator that creates a .cpp file for you to compile:</p> <pre><code>#!/usr/bin/env python with file('bar.cpp', 'w') as f: f.write('void bar(int i) {\n') f.write(' switch(i) {\n') for i in range(50): f.write(' case %d: foo(userInput&lt;%d&gt;::typeName()); return;\n' % (i, i)) f.write(' default: throw someException;\n') f.write(' }\n') f.write('}\n') </code></pre> <p>Yet another alternative is to create a lookup array (or vector) that's initialized with the appropriate objects/functions/whatever, so you can use *userInputLookup[i] in place of userInput. But without knowing the exact use case, and whether you're using C++11, it's hard to give details.</p>
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