Re: [boost] [iterators] Proof-of-concept for a sentinel iterator adapter

Subject: Re: [boost] [iterators] Proof-of-concept for a sentinel iterator adapter
From: Beman Dawes (bdawes_at_[hidden])
Date: 2009-05-13 17:06:03

On Wed, May 13, 2009 at 12:38 PM, Simonson, Lucanus J
<lucanus.j.simonson_at_[hidden]> wrote:
> Thorsten Ottosen wrote:
>> joaquin_at_[hidden] skrev:
>>> Beman Dawes escribió:
>>>> Attached is proof-of-concept code for a sentinel iterator adapter.
>>>> It turns a pointer to sentinel terminated sequence, such as a
>>>> C-style string, into a forward iterator with a conforming end
>>>> iterator.
>>>>
>>>
>>> Having Sentinel specified as a non-type template parameter greatly
>>> reduces the category of types this can work with. I'd replace it
>>> with some SentinelFactory policy or something.
>>
>> That is not a bad idea, although it would really be good if
>> the basic case can stay as optimaized as currently
>> (having a static member). I guess having a static member is
>> not an option for a general policy, thus giving us the usual
>> iterator problem of double storage.
>>
> I don't understand the rationale for m_sentinel.  Couldn't the code refer to Sentinel directly as a compile time constant as opposed to a static member variable?

The concern is that Sentinel() isn't a compile time constant. It is a
potentially expensive call to a constructor. An optimizer may be smart
enough to resolve Sentinel() at compile time, and generate maximally
efficient code accordingly, but there is no guarantee of that.

--Beman