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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Rejects valid: reading of an inactive union member that shares common initial sequence with the active one"
href="https://bugs.llvm.org/show_bug.cgi?id=43921">43921</a>
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<th>Summary</th>
<td>Rejects valid: reading of an inactive union member that shares common initial sequence with the active one
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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>All
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Keywords</th>
<td>compile-fail
</td>
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<th>Severity</th>
<td>normal
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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>nok.raven@gmail.com
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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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<pre>The wording is in [class.union]/1 and [class.mem]/25.
[class.mem]/25 contains an example:
struct T1 { int a, b; };
struct T2 { int c; double d; };
union U { T1 t1; T2 t2; };
int f() {
U u = { { 1, 2 } }; // active member is t1
return u.t2.c; // OK, as if u.t1.a were nominated
}
Running this example in constexpr context, or just turning the `f` into a
constexpr function produces an error:
<source>:4:15: error: constexpr function never produces a constant expression
[-Winvalid-constexpr]
constexpr int f() {
^
<source>:6:10: note: read of member 't2' of union with active member 't1' is
not allowed in a constant expression
return u.t2.c; // OK, as if u.t1.a were nominated
^
1 errors generated.</pre>
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