<html>
<head>
<base href="http://bugs.llvm.org/">
</head>
<body><span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - constexpr variable template requires default initialization even though it's not instantiated"
href="http://bugs.llvm.org/show_bug.cgi?id=32115">bug 32115</a>
<br>
<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>INVALID
</td>
</tr>
<tr>
<td style="text-align:right;">CC</td>
<td>
</td>
<td>richard-llvm@metafoo.co.uk
</td>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr></table>
<p>
<div>
<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - constexpr variable template requires default initialization even though it's not instantiated"
href="http://bugs.llvm.org/show_bug.cgi?id=32115#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - constexpr variable template requires default initialization even though it's not instantiated"
href="http://bugs.llvm.org/show_bug.cgi?id=32115">bug 32115</a>
from <span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span></b>
<pre>[temp.res]p8: "The program is ill-formed, no diagnostic required, if [...] no
valid specialization can be generated for a template and the template is not
instantiated."
<span class="quote">> that would be consistent with a constexpr function for example that
> can remain undefined unless it's actually used.</span >
Clang rejects this case too, for the same reason:
template<typename T> constexpr void f() {
const int n;
}
<span class="quote">> Eventually, I'm looking to specialize the tag for different type and
> letting the compile catch any untagged types.</span >
This only triggers a warning (and a link error), but here's a valid way to get
something like what you want:
template<typename T> extern int kTag;
template<> constexpr int kTag<int> = 0;</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>