On Friday, 4 April 2025 11:15:35 Pacific Daylight Time Thiago Macieira wrote:
> BTW, I said we "have the same problem with QMetaType", but in reality we
> don't because we take this into account.
> friend bool comparesEqual(const QMetaType &lhs,
> const QMetaType &rhs)
> {
> if (lhs.d_ptr == rhs.d_ptr)
> return true;
> if (!lhs.d_ptr || !rhs.d_ptr)
> return false; // one type is undefined, the other is defined
> // avoid id call if we already have the id
> const int aId = lhs.id();
> const int bId = rhs.id();
> return aId == bId;
> }
libstdc++'s type_info has similar code:
_GLIBCXX23_CONSTEXPR inline bool
type_info::operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
{
if (std::__is_constant_evaluated())
return this == &__arg;
if (__name == __arg.__name)
return true;
#if !__GXX_TYPEINFO_EQUALITY_INLINE
// ABI requires comparisons to be non-inline.
return __equal(__arg);
#elif !__GXX_MERGED_TYPEINFO_NAMES
// Need to do string comparison.
return __name[0] != '*' && __builtin_strcmp (__name, __arg.name()) == 0;
#else
return false;
#endif
}
I just don't know when it emits that * prefix. I've seen them before, but I
don't recall the details of how it works. The GCC source code uses
TREE_PUBLIC() but I don't understand how to set it.
libc++ does not have that: their std::type_info::operator== only compares the
type_name pointer address on non-Windows systems (see the definition of the
_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION macro in <typeinfo>).
--
Thiago Macieira - thiago.macieira (AT) intel.com
Principal Engineer - Intel DCAI Platform & System Engineering
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