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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 --- - error: non-type template argument is not a constant expression (GCC compiles, clang doesn't)"
href="https://llvm.org/bugs/show_bug.cgi?id=28711">28711</a>
</td>
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<th>Summary</th>
<td>error: non-type template argument is not a constant expression (GCC compiles, clang doesn't)
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.8
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>weiss@wsoptics.de
</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>I believe that the following code is valid C++14 and should compile. GCC 5.4.0
does compile it without warnings:
-----------------------
#include <array>
#include <cstddef>
#include <utility>
namespace detail {
namespace detail {
template<typename R, typename F, typename A, std::size_t... index>
constexpr decltype(auto) func_apply_impl(F && f, A && a,
std::index_sequence<index...>)
{
return R{f(std::forward<A>(a)[index])...};
}
}
//! Take an object a of type A that has size() and operator[] and return
R{f(a[0]), ..., f(a[a.size()-1])}
template<typename R, typename F, typename A>
constexpr decltype(auto) func_apply(F && f, A && a)
{
return detail::func_apply_impl<R>(std::forward<F>(f),
std::forward<A>(a), std::make_index_sequence<a.size()>{});
}
}
template<typename T, std::size_t N> constexpr auto operator*(T const t,
std::array<T, N> const & rhs) { return detail::func_apply<std::array<T, N>>([t]
(const auto r) { return t * r; }, rhs); }
int main()
{
const std::array<int, 3> a{1, 2, 3};
const auto b = 2 * a;
return 0;
}
----------------------
It might be related to 28385, but it behaves the same with both --std=c++14 and
--std=c++1z
clang 3.8.1 gives:
/tmp/z.cpp:17:103: error: non-type template argument is not a constant
expression
return detail::func_apply_impl<R>(std::forward<F>(f),
std::forward<A>(a), std::make_index_sequence<a.size()>{});</pre>
</div>
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