Re: [review] [STLInterfaces] STLInterfaces iterator_interface mini mini review

From: Zach Laine (whatwasthataddress_at_[hidden])
Date: 2019-12-18 02:24:21

On Tue, Dec 17, 2019 at 9:59 AM Arthur Gruzauskas via Boost <
boost_at_[hidden]> wrote:

> On Wednesday, 11 December 2019 11:21:23 AM AEDT Barrett Adair via Boost
> wrote:
>
> > Dear Boost,
> >
> > The formal review of Zach Laine's STLInterfaces library begins now, and
> > will run through December 19. Please participate in this review if you
> can.
> > To submit a review, please reply to this email with the following
> > information:
> > - Your name
>
> Arthur Gruzauskas
>

Thanks for the review, Arthur!

[snip]

> - Did you attempt to use the library? If so:
>
> >   * Which compiler(s)?
>
> clang-8 for c++17 on debian linux.
>
> >   * What was the experience? Any problems?
>
> very straightforward.
>
> a few small glitches, as I just grabbed  iterator_interface.hpp and
> fwd.hpp
> and made small changes for it to work inside my project.
>
> https://github.com/tzlaine/stl_interfaces/issues  describes two minor
> issues,
> which could be well related to me just grabbing those 2 files only,
> outside the
> boost structure that would normally sustain it.
>

For others following this, these issues are resolved for me locally, but
will not appear publicly during the review.  The issue is a missing
defined() in a couple of preprocessor expressions.

[snip]

> My one small concern is in the required method:
>
> constexpr auto operator-(repeated_chars_iterator other) const noexcept
>
> instead of:
>
> constexpr auto operator-(const repeated_chars_iterator& other) const
> noexcept
>
> I may soon have a need for an iterator that holds a lot of state, and
> copying
> that iterator for each subtraction makes me wonder about a performance
> penalty
> in inner loops.
>
> It is not a dealbreaker for this review, and I didn't examine Zach's
> tradeoffs
> for doing it this way. I see many of my use cases where this approach will
> be
> fine.
>

In short, I'm doing this for two reasons:

1) An iterator type is typically the size of a pointer or maybe two, and so
pass-by-value is usually more optimal than pass-by-reference.
2) All the STL interfaces that take iterators do it this way, and so making
the STLInterfaces usage pass-by-reference probably won't affect >= 90% of
your uses of a given iterator type.

Zach