Re: Weird behaviour from std::list<>::reverse_iterator
On Aug 26, 2:48 pm, Pete Becker <p...@versatilecoding.com> wrote:
James Kanze wrote:
That, on the other hand, could be done. As far as I know,
no one has suggested it, but it would certainly be possible
to overload list<>::erase (and the erase functions in the
other containers) to take a reverse iterator, and that these
overloaded functions encapsulate the necessary logic.
Well, sure. We could add erase member functions that take each
of the standard's iterator adaptors to every container. But
that won't help with user-defined iterator adaptors.
You're thinking too generically. std::list<> has functions
which return a std::list<>::reverse_iterator, so it doesn't seem
too far fetched to say that such an iterator can be used to
specify the location for insertion or erasure.
I think that would be a minimum extension, and not to difficult.
Handling arbitrary adapters would be a major project---it might
be nice, but I'd like to see a proof of concept implementation
first.
Isn't that the philosophy behind the STL?
Not really. The philosophy is generally let the user
beware, with undefined behavior lurking at every (mis)step.
When a program calls list::erase with a reverse iterator the
requirement is clear. list::erase takes an argument of type
list::const_iterator, so the program is ill-formed. No
undefined behavior in sight.
In this case:-).
And in the current standard, list::erase takes an iterator, and
not a const_iterator. Changing that (rather than adding an
overload) breaks user code, e.g.:
template< typename T >
class MyIterator
{
public:
operator std::list< T >::iterator() const
{
return something ;
}
// ...
} ;
void
f( std::list< int >& l )
{
MyIterator i( ... ) ;
l.erase( i ) ;
}
According to C++03, that's legal code, and guaranteed to work.
According to the draft C++0x, it's not, and requires a compiler
diagnostic.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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