Re: [PATCH] __debug::list use C++11 direct initialization

[François Dumont <frs dot dumont at gmail dot com>]

On 10/15/2018 12:07 PM, Jonathan Wakely wrote:
> On 09/10/18 07:11 +0200, François Dumont wrote:
> > Here is the communication for my yesterday's patch which I thought 
> > svn had failed to commit (I had to interrupt it).
> >
> > Similarly to what I've done for associative containers here is a 
> > cleanup of the std::__debug::list implementation leveraging more on 
> > C++11 direct initialization.
> >
> > I also made sure we use consistent comparison between 
> > iterator/const_iterator in erase and emplace methods.
> >
> > 2018-10-08  François Dumont <fdumont@gcc.gnu.org>
> >
> >     * include/debug/list (list<>::cbegin()): Use C++11 direct
> >     initialization.
> >     (list<>::cend()): Likewise.
> >     (list<>::emplace<>(const_iterator, _Args&&...)): Likewise.
> >     (list<>::insert(const_iterator, initializer_list<>)): Likewise.
> >     (list<>::insert(const_iterator, size_type, const _Tp&)): Likewise.
> >     (list<>::erase(const_iterator, const_iterator)): Ensure consistent
> >     iterator comparisons.
> >     (list<>::splice(const_iterator, list&&, const_iterator,
> >     const_iterator)): Likewise.
> >
> > Tested under Linux x86_64 Debug mode and committed.
> >
> > François
>
> > diff --git a/libstdc++-v3/include/debug/list 
> > b/libstdc++-v3/include/debug/list
> > index 8add1d596e0..879e1177497 100644
> > --- a/libstdc++-v3/include/debug/list
> > +++ b/libstdc++-v3/include/debug/list
> > @@ -244,11 +244,11 @@ namespace __debug
> > #if __cplusplus >= 201103L
> >       const_iterator
> >       cbegin() const noexcept
> > -      { return const_iterator(_Base::begin(), this); }
> > +      { return { _Base::begin(), this }; }
> >
> >       const_iterator
> >       cend() const noexcept
> > -      { return const_iterator(_Base::end(), this); }
> > +      { return { _Base::end(), this }; }
>
> For functions like emplace (which are C++11-only) and for forward_list
> (also C++11-only) using this syntax makes it clearer.
>
> But for these functions it just makes cbegin() and cend() look
> different to the C++98 begin() and end() functions, for no obvious
> benefit.
>
> Simply using { return end(); } would have been another option.
Personnaly I hesitated in writting:

{ return { _Base::cbegin(), this }; }

cause I prefer when you see clearly that Debug implem forward calls to 
the Normal implem.

I thought that using C++11 direct init was more likely to have gcc elide 
the copy constructor so I used it everywhere possible.