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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang fails to propagate constness to union member in template"
href="http://llvm.org/bugs/show_bug.cgi?id=22639">22639</a>
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<th>Summary</th>
<td>clang fails to propagate constness to union member in template
</td>
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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
</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>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>kaballo86@hotmail.com
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</tr>
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<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
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<pre>In the following snippet, clang doesn't propagate constness to the union member
in the marked line:
template <int I> struct _index {};
struct u1 {
u1(_index<0>, float v) : _head(v) {}
void get(_index<0>) {}
float const& get(_index<0>) const { return _head; }
float _head;
};
template <typename = void> // must be template
struct u2 {
u2(_index<0>, int v) : _head(v) {}
u2(_index<1>, float v) : _tail(_index<0>{}, v) {}
void get(_index<0>) {}
int const& get(_index<0>) const { return _head; }
void get(_index<1>) {}
float const& get(_index<1>) const { return _tail.get(_index<0>{}); } //
fails here
//float const& get(_index<1>) const { return
this->_tail.get(_index<0>{}); } // this works
union {
int _head;
u1 _tail;
};
};
struct variant {
variant(int i) : _storage{_index<0>{}, i}, _which(0) {}
variant(float f) : _storage{_index<1>{}, f}, _which(1) {}
template <int I> void const* target() const
{ return _which == I ? &_storage.get(_index<I>{}) : nullptr; }
u2<> _storage;
int _which;
};
int main() {
variant const sv(42.f);
sv.target<1>(); // note: requested here
}
This can be observed via the error message `reference to type 'const float'
could not bind to an rvalue of type 'void'`, showing that the non-const
overload of `_tail.get` was chosen. Using `this->_tail` instead works as
expected.</pre>
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