[boost] [filter_iterator] Why do filter_iterator constructors use default parameter values?

From: Jurko Gospodnetiæ (jurko_for_boost_at_[hidden])
Date: 2006-07-02 14:00:10

  Hi all.

  I was wondering why filter_iterator constructors allow
default parameter values? More precisely, if the end
iterator parameter is not given then the constructor silently
uses a default generated iterator as its internal end iterator.

  This interface seems dangerous to me and has caused
us one hard-to-track-down bug... because the
filter_iterator silently used an incorrect end iterator and
so sometimes managed to iterate passed the end of its
container... causing of course all sorts of cute
behaviour... :-) (access violations, random API call
failures, gibberish values read through the iterator...)
The failures themselves were also random enough to
make tracking this baby down a real pain in the
behind... :-)

  Now we are bigger & wiser, but I was still wandering
what the rationale was for using this interface? Why not
simply make the end iterator parameter be mandatory?
That would make it explicitly clear to the novice user
that he needs to specify the end iterator.

  If there actually is some reason for implementing
filter_iterators this way, could someone add a warning
or a rationale explanation regarding this in the official
documentation?

  Hope this helps...

  Best regards,
    Jurko Gospodnetiæ