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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang C++11 wrong number of template parameters using aliases with template parameter pack"
href="http://llvm.org/bugs/show_bug.cgi?id=20398">20398</a>
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<th>Summary</th>
<td>clang C++11 wrong number of template parameters using aliases with template parameter pack
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.4
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++11
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>reagentoo@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Bug appears when passing template parameter packs to aliases. As a result, the
alias does not accept any parameters without any warning from the compiler.
Minimal test-case:
==================
#include <string>
#include <iostream>
template <template <class...> class TT, class T, class... Rest>
using Tail = TT<Rest...>;
template <class... Ts>
struct Bar
{
static constexpr uint size = sizeof...(Ts);
};
template <class... Ts>
struct Foo
{
static constexpr uint size = sizeof...(Ts);
using TailBar = Tail<Bar, Ts...>;
static constexpr uint bar_size = TailBar::size;
};
int main(int argc, char *argv[])
{
using ZZZ = Foo<int, int, int>;
std::cout << "size:" << ZZZ::size << " bar_size:" << ZZZ::bar_size <<
std::endl;
}
==================
Expected output: "size:3 bar_size:2"
Resulting output: "size:3 bar_size:0"
This bug does not occur if we refuse to use an alias "Tail":
...
template <template <class...> class TT, class T, class... Rest>
struct Tail
{
using type = TT<Rest...>;
};
...</pre>
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