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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __cpp_nontype_template_args >= 201907L but floating-point template arguments rejected"
href="https://bugs.llvm.org/show_bug.cgi?id=49369">49369</a>
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<th>Summary</th>
<td>__cpp_nontype_template_args >= 201907L but floating-point template arguments rejected
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++2a
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>Casey@Carter.net
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Clang 12.0.0-rc2 (and trunk) define __cpp_nontype_template_args to 201907L
indicating support for P1907R1 "Inconsistencies with non-type template
parameters"
(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1907r1.html">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1907r1.html</a>). This
proposal changes the constraint on non-type template arguments to require that
they have structural type, or [other cases that aren't germane] (N4878
[temp.param]/6). A _structural_ _type_ is a scalar type, or [other cases that
aren't germane] (N4878 [temp.param]/7). Scalar types include floating-point
types (N4878 [basic.types.general]/9). Nonetheless, this well-formed TU:
template <auto> int f() { return 42; }
int main() {
#if defined(__cpp_nontype_template_args) && \
__cpp_nontype_template_args >= 201911L
return f<3.14>();
#endif
}
when compiled with "-std=c++2a" generates diagnostics:
<source>:6:12: error: no matching function for call to 'f'
return f<3.14>();
^~~~~~~
<source>:1:21: note: candidate template ignored: invalid
explicitly-specified argument for 1st template parameter
template <auto> int f() { return 42; }
^
1 error generated.
Is there any chance that either the implementation of P1907R1 could be
completed or the value of __cpp_nontype_template_args reduced (to indicate
incomplete support) in time for Clang 12?</pre>
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