Use C++11 direct init in __debug::forward_list

[François Dumont]

On 10/15/2018 11:58 AM, Jonathan Wakely wrote:
> On 11/10/18 22:46 +0200, François Dumont wrote:
>> This patch makes extensive use of C++11 direct init in 
>> __debug::forward_list.
>>
>> Doing so I also try to detect useless creation of safe iterators in 
>> debug implementation. In __debug::forward_list there are severals but 
>> I wonder if it is worth fixing those. Most of them are like this:
>>
>> Â Â Â Â Â  void
>> Â Â Â Â Â  splice_after(const_iterator __pos, forward_list& __list)
>> Â Â Â Â Â  { splice_after(__pos, std::move(__list)); }
>>
>> __pos is copied.
>>
>> Do you think I shouldn't care, gcc will optimize it ?
>
> I think the _Safe_iterator construction/destruction is too complex to
> be optimised away (it locks a mutex, doesn't it?).

Yes it does, I also would be surprised if gcc was able to optimize it away.

>
> Normally I'd say you could use std::move(__pos) but IIRC that's even
> more expensive than a copy, as it locks two mutexes.
>
>> I wonder if it would be ok in debug implementation to use this kind 
>> of signature:
>>
>> void splice_after(const const_iterator& __pos, forward_list& __list)
>>
>> Iterator taken as rvalue reference ?
>>
>> I guess it is not Standard conformant so not correct but maybe I 
>> could add a private _M_splice_after with this signature.
>
> It doesn't seem worthwhile to me.
>
>
Ok, I'll leave it this way.

Thanks,

François