[boost] Re: potential problem with indirect_iterator (GCC 3.3.2)

From: Tom Widmer (tom_usenet_at_[hidden])
Date: 2004-03-02 12:42:09

On Tue, 02 Mar 2004 09:23:36 -0500, David Abrahams
<dave_at_[hidden]> wrote:

>Tom Widmer <tom_usenet_at_[hidden]> writes:
>
>>>If I'm misusing the code, is there some reason for this?  It's
>>>inconvenient that the default constructor doesn't initialize pointers
>>>to some consistent value; the problem goes away when I change the
>>>indirect_iterator default constructor:
>>>
>>>    94c94,96
>>>    <       indirect_iterator() {}
>>>    ---
>>>    >       indirect_iterator()
>>>    >         : super_t( Iterator() )
>>>    >       {}
>>
>> That gives you a false sense of safety. Default initializing many
>> iterator types is a no-op - they are still unusable (e.g.
>> std::list::iterator).
>
>or, in the same way, int*.

Default initializing an int* isn't a no-op, and you can equality
compare such int*s. The same isn't true for std::list::iterator, which
is why I chose it.

e.g.
It i = It();
It j = It();
bool b = (i == j);

That's well defined for It=int* (and It=istream_iterator<T>), but UB
for It=std::list<int>::iterator (since i and j are singular).

Tom
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