[cfe-dev] When does ~decltype(expr) make sense ?

[Manasij Mukherjee]

So, an extra condition takes care of not allowing the decltype when
declaring the dtor.
! getCurScope()->isClassScope()

Am I correct ?

> you can use ~decltype(...)() to invoke a destructor
Why is that allowed?
And what exactly is a valid use of this ?

>From the report,
A().~decltype(auto); // ICE, and A can be an empty struct

Does the standard say anything about what can the decltype contain ?
Should the compiler figure something out from the auto here ?

On Tue, Feb 24, 2015 at 12:26 AM, Richard Smith <richard at metafoo.co.uk>
wrote:

> On Sun, Feb 22, 2015 at 3:24 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>>
>>
>> On Sun, Feb 22, 2015 at 2:33 PM, Manasij Mukherjee <manasij7479 at gmail.com
>> > wrote:
>>
>>>
>>>
>>>> 5.1.1 [expr.prim.general] in paragraph 8 states that "The form ~
>>>> decltype-specifier also denotes the destructor, but it shall not be used as
>>>> the unqualified-id in a qualified-id."
>>>>
>>>> I implemented this a while ago, but it looks like (r146155) it was for
>>>> expressions (x.~decltype(*x)(), for example) not necessarily for dtor
>>>> declarations.
>>>>
>>>> I do not clearly understand what this sentence implies.
>>> Could you elaborate?
>>>
>>> Also, if the meaning is as you interpreted it, what is the rationale for
>>> allowing x.~decltype(*x)() ?
>>>
>>
>> Not quite sure I understand this question (though I did make a mistake in
>> that example, should've been x->~decltype(*x)())
>>
>
> That doesn't work either: decltype(*x) is a reference type. It'd need to
> be something ridiculous like
>
>   X x;
>   x.~decltype(x)();
>   new (&x) X;
>
> 5.1.1 talks about how ~decltype(...) is a valid unqualified id, except in
>> the case of a qualified id (ie, you can't write "x::y::~decltype(...)"). So
>> that's how x->~decltype(*x)() is valid, as far as I see/read/understand it
>> - wherever you can use an unqualified-id that would name a dtor, you can
>> use ~decltype(...) too (ecxept in the qualified-id case).
>>
>
> Right; you can use ~decltype(...)() to invoke a destructor, but you can't
> use ~decltype to declare a destructor.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20150224/4aa4f4bc/attachment.html>