[LLVMbugs] [Bug 9882] New: noexcept sometimes returns unexpected value

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon May 9 13:46:38 PDT 2011


           Summary: noexcept sometimes returns unexpected value
           Product: clang
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++0x
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: hhinnant at apple.com
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com

#include <iostream>

template <class T, T v>
struct integral_constant
    static const T value1 = v;

template <class T>
T&& declval() noexcept;

template <class T, class U>
struct is_nothrow_assignable
    : public integral_constant<bool, noexcept(declval<T>() = declval<U>())>
    static const bool value2 = noexcept(declval<T>() = declval<U>());

int main()
    std::cout << is_nothrow_assignable<int&, int&>::value1 << '\n';
    std::cout << is_nothrow_assignable<int&, int&>::value2 << '\n';

I'm getting:


I'm expecting:


It seems like the noexcept wrongly evaluates to false when used in specifying
the base class.

With this fixed, I think I can implement the nothrow type traits without
compiler support as long as the associated non-nothrow type traits are working.

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