http://llvm.org/bugs/show_bug.cgi?id=22639
Bug ID: 22639
Summary: clang fails to propagate constness to union member in
template
Product: clang
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
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.
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