libstdc++/41975

[Daniel Krügler]

2011/11/22 Daniel Krügler <daniel.kruegler@googlemail.com>:
> 2011/11/22 François Dumont <frs.dumont@gmail.com>:
>> Hi
>>
>> Here is my latest proposition to fix 41975 defect.
>>
>> Now all tests are passing under linux x86_64. There is no ICE anymore, I
>> don't know where they were coming and I haven't been able to reproduce, a
>> bad build perhaps.
>>
>> There is now the static_assert to check that hash code is cache or that the
>> hash functor is noexcept qualified. The hash codes are cached only where the
>> type is not an integral type and when the hash functor do not throw.
>>
[..]

>> Ok to commit in trunk ?
>
> Regarding:
>
> +      static_assert(__or_<integral_constant<bool, __cache_hash_code>,
> +                     integral_constant<bool,
> +                       noexcept(declval<const _H1&>()(declval<const _Key&>()))>
> +                        >::value,
> +           "Cache the hash code or qualify your hash functor with noexcept");
>
> I would recommend to wrap the expression test in a wrapper trait combined
> to ensure lazy evaluation. As written, this test is always performed, regardless
> of the value of __cache_hash_code.

Same issue in include/bits/unordered_map.h (twice):

+	   bool __cache_hash_code =
+	     __not_<__and_<is_integral<_Key>,
+			   integral_constant<bool,
+		noexcept(declval<const _Hash&>()(declval<const _Key&>()))>>
+		   >::value>

and in unordered_set.h (twice):

+	   bool __cache_hash_code =
+	     __not_<__and_<is_integral<_Value>,
+			   integral_constant<bool,
+		  noexcept(declval<const _Hash&>()(declval<const _Value&>()))>>
+		   >::value>

- Daniel