JOAQUIN LOPEZ MU?Z wrote:
----- Mensaje original ----- De: Peter Dimov <pdimov@mmltd.net> Fecha: Viernes, Mayo 27, 2005 11:10 pm Asunto: Re: [boost] Re: compressed_pair requirements?
JOAQUIN LOPEZ MU?Z wrote:
IMHO, std::pair default ctor should be defined as
pair():first(),second(){}
This doesn't change things. pair() {} is what you probably want.
Why? (This is not a rethoric question, my understanding of value-initialization matters is so poor.)
Never mind, I probably didn't understand your intent. The above does indeed eliminate the problem with the iterator while still leaving PODs zero-initialized. pair() {} will leave PODs uninitialized.
I think there's some value in having iterators being DefaultConstructible. Otherwise you're forced to have some container around everytime you construct an iterator.
I think that this is not that restrictive as it sounds, because an iterator logically belongs to a container; it has no value on its own. A single containerless iterator can be replaced by a pointer. An iterator range is, of course, useful on its own, but you can't create a containerless range, even an empty one, because...
Defaut construction for iterators is roughly the equivalent of initializing to 0 in the case of pointers.
... default-constructed iterators are useless. A NULL pointer is copyable and you can compare a NULL to another pointer, with well-defined results (so you can make an empty range from two NULL pointers). Default construction for iterators is a trap. :-)