<br><br><div class="gmail_quote">On Thu, Dec 13, 2012 at 11:56 AM, js.mdnq <span dir="ltr"><<a href="mailto:js_adddot+mdng@gmail.com" target="_blank">js_adddot+mdng@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I need to get the number of type parameters of a class at compile time:<br>
<br>
<br>
class a(T1, T2, ...)<br>
{<br>
static if (a.TypeInfo.NumParameters == 1)<br>
....<br>
else<br>
....<br>
<br>
}<br>
<br>
Is this possible?<br>
</blockquote></div><br><div>Yes, it's possible: </div><div><br></div><div>// Inside the class, it's easy:</div><div>class Test(T...)</div><div><div>{</div><div> enum num = T.length;// T is known here</div><div>
}</div><div><br></div><div>// Outside the class, it's a bit tricky, but quite doable:</div><div>template TemplateArity(Type)</div><div>{</div><div> enum T = Type.stringof;</div><div> mixin("alias " ~ T ~ " U;");</div>
<div> static if (is(Type _ == U!Args, Args...))</div><div> enum TemplateArity = Args.length;</div><div> else</div><div> enum TemplateArity = -1;</div><div>}</div><div><br></div><div>void main()</div><div>
{</div><div> alias Test!(int, double, string) T;</div><div><br></div><div> assert(T.num == 3); // Internal knowledge</div><div> assert(TemplateArity!T == 3); // External deduction</div><div>}</div></div><div><br>
</div>