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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 --- - Superfluous instantiations during std::async overload resolution" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23700&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=glmlgren1rpJrJtUCPLUYp7XGAhX_-TGNfD_f802Y8M&s=6v6fgpQ9WxyGqqCx5aLyCJP4AqtkFpOwmt4c_1Q3NzI&e=">23700</a>
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<th>Summary</th>
<td>Superfluous instantiations during std::async overload resolution
</td>
</tr>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>kaballo86@hotmail.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu, mclow.lists@gmail.com
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The following snippet triggers a compilation failure:
#include <future>
#include <type_traits>
struct foo {
template <class ...Ts>
void operator()(Ts...) {}
};
struct bar {
template <class T>
struct result {
static_assert(!std::is_integral<T>::value, "nope");
using type = T;
};
template <class T>
typename result<T>::type operator()(T v) { return v; }
};
int main() {
std::async(foo(), bar(), 42);
}
During overload resolution, the `async` overload taking a `launch` policy as
first argument is trying to instantiate `bar::operator()(int)` declaration,
resulting in an error that's not in the immediate context.
This snippet might be ill-formed given [temp.inst]/7
<span class="quote">> If the overload resolution process can determine the correct function to call without instantiating a class template definition, it is unspecified whether that instantiation actually takes place.</span ></pre>
</div>
</p>
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