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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 --- - Conditional expression accepted despite ambiguous common type: derived-to-base and base-to-derived UDC"
href="https://llvm.org/bugs/show_bug.cgi?id=23006">23006</a>
</td>
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<tr>
<th>Summary</th>
<td>Conditional expression accepted despite ambiguous common type: derived-to-base and base-to-derived UDC
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</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++11
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hstong@ca.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Conditional expressions where the second and third operands have different
types are ill-formed if conversion can be done both ways.
Clang fails to reject the conditional expression in the case below where one
conversion is derived-to-base with slicing and the other is a user-defined
conversion.
In the case below, this manifests as an error because the wrong partial
specialization is chosen.
### SOURCE (<stdin>):
struct A;
struct B {
operator A &&();
} bObj;
struct A : B { };
enum E { Gnat };
A &&fooA(E);
bool b;
template <typename T, typename U = char [sizeof 0]> struct Hack { };
template <typename T> struct Hack<T, char [sizeof ((b ? bObj : fooA(T())),
0)]>;
void bar() {
A &&t1 = bObj;
B t2 = fooA(Gnat);
Hack<E> hack;
}
### COMPILER INVOCATION:
clang++ -cc1 -std=c++11 -x c++ -
### ACTUAL OUTPUT:
<stdin>:20:12: error: implicit instantiation of undefined template 'Hack<E,
char [4]>'
Hack<E> hack;
^
<stdin>:15:30: note: template is declared here
template <typename T> struct Hack<T, char [sizeof ((b ? bObj : fooA(T())),
0)]>;
^
1 error generated.
### EXPECTED OUTPUT:
(Successful compile).
### COMPILER VERSION INFO:
clang version 3.7.0 (trunk 232951)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation:
/usr/local/gcc-4.8.2/lib/gcc/x86_64-unknown-linux-gnu/4.8.2
Selected GCC installation:
/usr/local/gcc-4.8.2/lib/gcc/x86_64-unknown-linux-gnu/4.8.2
Candidate multilib: .;@m64
Selected multilib: .;@m64</pre>
</div>
</p>
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