Re: "Reader" as alternative to Iterator

On Sa, 2017-07-01 at 19:38 +0200, Andreas Hennings wrote: > Hello internals, > (this is my first email to this list, hopefully I'm doing ok.) > > ------------------------------------------------------------------- > ------------- > > Background / motivation: > > Currently in PHP we have an interface "Iterator", and a final class > "Generator" > (and others) that implement it. > > Using an iterator in foreach () is straightforward: > foreach ($iterator as $key => $value) {..} > > However, if we want to iterate only a portion and then continue > elsewhere at the position where we stopped, we need to do something > like this: > > for ($iterator->rewind(); $iterator->valid(); $iterator->next()) { >   $value = $iterator->current(); >   [..] > } > > This is unpleasantly verbose, and also adds performance overhead due > to additional function calls. Wouldn't SPL's NoRewindIterator be enough? $nit = new NoRewindIterator($it); foreach ($nit as $row) {  break; } foreach ($nit as $row) {   // continues same iteration } > > Also, manually writing an iterator is quite painful. > > I sometimes implement "readers" that can be used like this (*): > > // Gets a reader at position zero. > $reader = $readerProvider->getReader(); > while (FALSE !== $value = $reader->read()) { >   [..] > } > > (*) Note that I am using FALSE as an equivalent for "end of data". Of > course it would be nice if we had a dedicated constant for this, that > does not constrain the range of possible values of the iterator. That distinction is the reason why next() and valid() are different methods in iterators. johannes