Re: [boost] Result of boost::split against empty string changed in post-1.45 release

Subject: Re: [boost] Result of boost::split against empty string changed in post-1.45 release
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2012-06-12 04:19:43

On 12 June 2012 04:48, Marshall Clow <mclow.lists_at_[hidden]> wrote:
> On Jun 11, 2012, at 1:26 PM, Mateusz Loskot wrote:
>> On 11 June 2012 19:09, Pavol Droba <droba_at_[hidden]> wrote:
>>> On Mon, 11 Jun 2012 16:58:40 +0200, Mateusz Loskot <mateusz_at_[hidden]> wrote:
>>>>
>>>> I have a simple program runs boost::split against empty string.
>>>> I'm testing with Boost 1.45 and later versions like 1.46 or 1.49.
>>>> As stated in the // comment below, there is difference in behaviour
>>>> depending on the Boost version:
>>>>
>>>> // https://gist.github.com/2910461
>>>> #include <cassert>
>>>> #include <string>
>>>> #include <vector>
>>>> #include <boost/algorithm/string/split.hpp>
>>>> #include <boost/algorithm/string/classification.hpp>
>>>>
>>>> int main(int argc, wchar_t* argv[])
>>>> {
>>>> Â  Â std::wstring s;
>>>> Â  Â std::vector<std::wstring> a;
>>>>
>>>> Â  Â assert(s.empty());
>>>> Â  Â boost::split(a, s, boost::is_any_of(L", "), boost::token_compress_on);
>>>> Â  Â // Boost 1.45: Â true
>>>> Â  Â // Boost 1.46+: false
>>>> Â  Â // Â  Assertion failed: s.empty() == a.empty(), file
>>>> boost_split_empty_string.cpp, line 16
>>>> Â  Â assert(s.empty() == a.empty());
>>>> Â  Â return 0;
>>>> }
>>>>
>>>> IMHO, the behaviour exposed in newer versions is a bug.
>>>> Could anyone shed light on what happened in post-1.46?
>>>
>>>
>>> Please search the boos archives. There was an extensive discussion about
>>> this particular issue.
>>
>> Pavol,
>>
>> You are right, there are some discussions about this behavior,
>> For example
>>
>> http://lists.boost.org/Archives/boost/2005/01/79380.php
>> https://svn.boost.org/trac/boost/ticket/534
>>
>> and others. Thanks for pointing that.
>>
>> I have to admit that to me the current behavior is not intuitive.
>> Also, I have failed to find any example of it in the docs.
>
>
> Mateusz --
>
> If you would be willing to write up a paragraph making this clear, I will put it into the docs.

Marshall,

I'd rather leave it to those who introduce changed behaviour, because
they're aware of all reasons behind it.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net