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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - deduction fails to extend explicitly-specified parameter pack in mixed specified/unspecified deduction"
href="https://llvm.org/bugs/show_bug.cgi?id=31580">31580</a>
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<th>Summary</th>
<td>deduction fails to extend explicitly-specified parameter pack in mixed specified/unspecified deduction
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<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>
<tr>
<th>Reporter</th>
<td>richard-llvm@metafoo.co.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Testcase:
template<typename T, typename U> struct pair {};
template<typename ...T, typename ...U> void f(pair<T, U>...); //
expected-error 0-2{{C++11}}
void g(pair<int, char> a, pair<long, double> b) { f<int>(a, b); }
template<int T, typename U> struct pairI {};
template<int ...T, typename ...U> void fI(pairI<T, U>...); // expected-error
0-2{{C++11}}
void g(pairI<0, char> a, pairI<1, double> b) { fI<0>(a, b); }
template<typename T, typename U> struct pair2 {};
template<template<typename,typename> class T, typename U> struct pairT {};
template<template<typename,typename> class ...T, typename ...U> void
fT(pairT<T, U>...); // expected-error 0-2{{C++11}}
void g(pairT<pair, char> a, pairT<pair2, double> b) { fT<pair>(a, b); }
Deduction fails in each case because we're unable to extend an unexpanded
partially-substituted parameter pack during template argument deduction.</pre>
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