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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Default argument of constexpr functions not usable in template using?"
href="https://bugs.llvm.org/show_bug.cgi?id=48222">48222</a>
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<th>Summary</th>
<td>Default argument of constexpr functions not usable in template using?
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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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++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>lf-bt@thax.hardliners.org
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>See the following code.
The error message is not helpful, either: the default argument is declared
earlier, and when given explicitly (-> workaround) the compiler has no
problems.
--- also <a href="https://godbolt.org/z/1b7h6b">https://godbolt.org/z/1b7h6b</a> :
struct foo {
static constexpr int max(int idx, int min = 0) {
return (idx > min) ? idx : min;
}
template <int I>
using slice = decltype(max(I)); // fails only in clang
// using slice = decltype(max(2)); // also fails in gcc trunk, but not gcc
10.2
// using slice = decltype(max(2, 0)); // workaround
};
---
<source>:7:26: error: use of default argument to function 'max' that is
declared later in class 'foo'
using slice = decltype(max(I)); // fails only in clang
^
<source>:2:47: note: default argument declared here
static constexpr int max(int idx, int min = 0) {
^</pre>
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