[cxx-abi-dev] Mangling sizeof

[John H. Spicer]

On Mar 9, 2009, at 12:31 PM, Doug Gregor wrote:

> On Mon, Mar 9, 2009 at 8:29 AM, John H. Spicer <jhs at edg.com> wrote:
>>
>> On Mar 9, 2009, at 11:21 AM, Doug Gregor wrote:
>>
>>> On Sun, Mar 8, 2009 at 12:32 PM, John H. Spicer <jhs at edg.com> wrote:
>>>>
>>>>
>>>> Is there any reason not to just say that doing substitution on an  
>>>> lambda
>>>> expression results in a substitution failure?
>>>
>>> Implementation cost, for one. We currently have to be able to  
>>> recover
>>> from a substitution failure in any expression or type. If we say  
>>> that
>>> substitution into a lambda cannot result in a hard error, it means
>>> that we have to be able to recover from substitution failures in any
>>> statement that occurs in the lambda.
>>>
>>
>> No, what I'm saying is that you never actually attempt the  
>> substitution.
>> If you encounter a lambda expression when doing substitution you  
>> just always
>> fail.
>
> Oh. So a function template like, e.g.,
>
>  template<typename T> void f(A<sizeof([](int) { return 0; })> *a = 0);
>
> could never be instantiated or invoked. In that case, I'd rather just
> ban the use of lambdas in sizeof and decltype. Issue 766 deals with
> this, and a favorable resolution there could make this
> mangling-the-body-of-a-lambda issue go away.
>
>

That works for me.

John.