https://bugs.llvm.org/show_bug.cgi?id=33089
Bug ID: 33089
Summary: Static value in depended class is treated as
non-constant expression.
Product: clang
Version: 3.9
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: C++11
Assignee: unassignedclangb...@nondot.org
Reporter: tomasz...@gmail.com
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
For following code:
#include <type_traits>
template<typename U, typename T>
decltype(U{T::value}) foo(T, int) { return T::value; }
template<typename U, typename T>
U foo(T, ...) = delete;
int main()
{
foo<short>(std::integral_constant<int, 20>{}, 0);
}
Candidate foo(T, int) is ignored with following error:
substitution failure [with U = short, T = std::__1::integral_constant<int,
20>]: non-constant-expression cannot be narrowed from type 'int' to 'short' in
initializer list decltype(U{T::value}) foo(T, int) { return T::value; }
As suggested the T::value is not constexpr expression, despite declared as
constexpr.
If the declaration is changed to us an compile time conversion operator, the
expression is properly regonized as compile time constant, and brace
initialization is well-formed.
template<typename U, typename T>
decltype(U{T{}}) foo(T, int) { return T::value; }
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