[cfe-commits] [libcxx] r104850 - in /libcxx/trunk: include/ src/ test/language.support/support.exception/except.nested/

[Sebastian Redl]

On Thu, 27 May 2010 17:06:52 -0000, Howard Hinnant <hhinnant at apple.com>
wrote:
> Author: hhinnant
> Date: Thu May 27 12:06:52 2010
> New Revision: 104850
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=104850&view=rev
> Log:
> [except.nested]
> 
> +template <class _E>
> +inline
> +void
> +rethrow_if_nested(const _E& __e, typename enable_if<
> +                                   !is_same<_E,
nested_exception>::value
> &&
> +                                   is_convertible<_E*,
> nested_exception*>::value
> +                                                   >::type* = 0)
> +{
> +    static_cast<const nested_exception&>(__e).rethrow_nested();
> +}
> +
> +template <class _E>
> +inline
> +void
> +rethrow_if_nested(const _E& __e, typename enable_if<
> +                                   is_same<_E, nested_exception>::value
||
> +                                   !is_convertible<_E*,
> nested_exception*>::value
> +                                                   >::type* = 0)
> +{
> +}

You don't seem to have any tests for this function. Anyway, unless I'm
missing something major, this is definitely wrong as implemented. Not only
does it only do a static switch on the type where the standard requires a
dynamic switch, the condition of the static switch is strange, too. Why is
the is_same case handled in the second function? It should be in the first.

But anyway, it doesn't work this way. What you need is:
1) One function to handle polymorphic types. In this one, you do a
dynamic_cast to nested_exception const* and call rethrow_nested() if it
succeeds. If nested_exception is in the direct inheritance path of _E, the
dynamic_cast is performed at compile time, so you don't have any efficiency
issues there (as if it matters here ...).
2) One function to handle non-polymorphic types. This needs to be a
separate function to avoid compile errors when applying dynamic_cast to
these types. Since nested_exception is polymorphic, any type that derives
from it is polymorphic too, so this function won't apply. If _E is not
directly derived from nested_exception and not polymorphic, then you
couldn't cross-cast to a nested_exception anyway, even if there is one in
the complete object. So this function is a no-op.

Sebastian