[cfe-dev] Usage of __for_bool_ value in __nat {} classes

[Eric Fiselier via cfe-dev]

@Erik, Thanks for digging through the history!

I still look forward to removing it after moving the SFINAE into the
template parameter list.

/Eric

On Tue, Jun 5, 2018 at 2:07 PM, Erik Pilkington <erik.pilkington at gmail.com>
wrote:

> Looks like the initial purpose was to implement a poor man's explicit
> operator bool that returned a pointer to member, but it was removed in
> r151088.
>
> On 2018-06-05 3:57 PM, Eric Fiselier via cfe-dev wrote:
>
> I'm not sure what the purpose is. I agree it doesn't seem to have any
> effect, and the git blame comes back to the initial commit for libc++.
> Changing the layout of `__nat` now would be an ABI break; so that's out of
> the question. But I have some upcoming patches that are going
> to remove most usages of it.
>
> @Howard, do you recall what the purpose of this was? Something to do with
> initializing empty structs maybe?
>
> /Eric
>
> On Tue, Jun 5, 2018 at 2:11 AM, Li, Zeyang via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> I was looking through clang's c++ standard library, and found this class
>> in the shared_ptr class.
>>
>> class shared_ptr
>> ...
>> private:
>>         struct __nat {int __for_bool_;};
>> ...
>> };
>>
>> and I understand that this class is used to detect whether type
>> conversion is possible at compile time, but its member __for_bool_ is never
>> used anywhere in the class or the weak_ptr counterpart. So my question is,
>> what is the point of __for_bool_, why not simply use an empty class for the
>> same purpose?
>>
>> I'm sure the standard library authors definitely knows better than me.
>> Please help.
>>
>> Thanks,
>> Zeyang
>>
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>>
>>
>
>
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