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    <h3>Preface</h3> <p>Two solutions will be found in this post, one using C++03 and the other C++11.</p> <p>It's hard (ie. you'll need to write a lot of code) if you'd like a true compile time <em>if</em> that is <strong>guaranteed</strong> not to have any runtime overhead what so ever (no function jumps, etc etc).</p> <p>It is however possible, though the code will be quite tedious to maintain if you feel like adding another option to it (in C++03). I'd recommend you to check out the below solutions.</p> <hr> <h3>Solution in C++03</h3> <p>Your compiler should be smart enough to optimize away any call to <code>LogHelper&lt;+NONE&gt;</code>, though if you are just looking for more readable code and not a superb performance gain this syntax is quite sweet.</p> <pre><code>enum LoggerType { NONE =0, DATE = (1&lt;&lt;0), TIME = (1&lt;&lt;1), PERCENT = (1&lt;&lt;2) }; template&lt;int&gt; void LogHelper (std::string&amp;); template&lt;&gt; inline void LogHelper&lt;+NONE&gt; (std::string&amp;) {} template&lt;&gt; inline void LogHelper&lt;+DATE&gt; (std::string&amp; s) {s += "1970-01-01 ";} template&lt;&gt; inline void LogHelper&lt;+TIME&gt; (std::string&amp; s) {s += "12:01:01 ";} template&lt;&gt; inline void LogHelper&lt;+PERCENT&gt; (std::string&amp; s) {s += "42% ";} template&lt;int LOG_FLAG = NONE&gt; struct Logger { static void log (std::string const&amp; description) { std::string s1; LogHelper&lt;DATE &amp; LOG_FLAG&gt; (s1); LogHelper&lt;TIME &amp; LOG_FLAG&gt; (s1); LogHelper&lt;PERCENT &amp; LOG_FLAG&gt; (s1); std::cerr.width (25); std::cerr &lt;&lt; s1 &lt;&lt; " &gt;&gt; " &lt;&lt; description &lt;&lt; std::endl; } }; </code></pre> <p>...</p> <pre><code>int main (int argc, char * argv[]) { Logger&lt;DATE|TIME|PERCENT&gt; foo_log; Logger&lt;TIME&gt; time_log; Logger&lt;&gt; no_log; time_log.log ("log objects initialized!"); foo_log .log ("using foo_log"); no_log .log ("about to terminate application"); } </code></pre> <p><strong>output</strong></p> <pre><code> 12:01:01 &gt;&gt; log objects initialized! 1970-01-01 12:01:01 42% &gt;&gt; using foo_log &gt;&gt; about to terminate application </code></pre> <hr> <h3>Solution using Variadic Templates (C++11)</h3> <pre><code>enum LoggerType { NONE, PERCENT, DATE, TIME }; template&lt;LoggerType T = NONE, LoggerType ... Next&gt; std::string LogHelper () { return LogHelper&lt;T&gt; () + "; " + LogHelper&lt;Next...&gt; (); } template&lt;&gt; std::string LogHelper&lt;NONE&gt; () {return ""; } template&lt;&gt; std::string LogHelper&lt;DATE&gt; () {return "1970-01-01";} template&lt;&gt; std::string LogHelper&lt;TIME&gt; () {return "00:01:42";} template&lt;&gt; std::string LogHelper&lt;PERCENT&gt; () {return "42%";} template&lt;LoggerType ... Types&gt; struct Logger { static void log (std::string const&amp; description) { std::cerr.width (25); std::cerr &lt;&lt; LogHelper&lt;Types...&gt; (); std::cerr &lt;&lt; " &gt;&gt; " &lt;&lt; description; std::cerr &lt;&lt; std::endl; } }; </code></pre> <p>...</p> <pre><code>int main (int argc, char * argv[]) { Logger&lt;DATE,TIME,PERCENT&gt; foo_log; Logger&lt;TIME&gt; time_log; Logger&lt;&gt; no_log; time_log.log ("log objects initialized!"); foo_log .log ("using foo_log"); no_log .log ("about to terminate application"); } </code></pre> <p><strong>output</strong></p> <pre><code> 00:01:42 &gt;&gt; log objects initialized! 1970-01-01; 00:01:42; 42% &gt;&gt; using foo_log &gt;&gt; about to terminate application </code></pre>
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    1. USFilip Roséen - refp
    1. USFilip Roséen - refp
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    1. COWhy is there a + in front of NONE, DATA etc.? I have never seen that before... (and it works, so I am assuming it has some meaning)
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    2. CO@Samaursa It's to implicitly cast the value of NONE, DATA, etc. to an *integer* instead of being a `enum LoggerType`, a shorter method than writing `static_cast<int> (NONE)`
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