Re: "Reader" as alternative to Iterator

On Mon, Jul 3, 2017 at 5:53 PM, Johannes Schlüter <johannes@schlueters.de> wrote: > On Mo, 2017-07-03 at 17:32 +0200, Niklas Keller wrote: > >> > That distinction is the reason why next() and valid() are different >> > methods in iterators. I would rather say this is the reason why current() and valid() are different methods. A combination of ->current() and next() would not cause problems. >> >> Not really, Iterator::next() returns void, so could as well return >> bool. > > Well, that story is a bit longer and I cut it short. Let's assume we > remove valid and use next's return value. Then we don't know if the > first element exists or not, as next is only called after the first > iteration. An alternative might be using only current() but then we > need a special, magic, return value to mark the end oder references. > Both are bad. The proposed ->read() method is more or less the same as ->current() plus ->next(), if ->current() always returns FALSE on end-of-data. An object that has both ->read() and ->valid() would remove the need for a special magic return value. But in many many cases, having a magic return value FALSE is totally acceptable. Think of fgetcsv(), fread(), or PDOStatement::fetch(). So if we wanted, we could have one interface "SimpleReader" or "FalseTerminatedReader" with only the ->read() method, and another method "Reader" with both ->read() and ->valid(). (Sometimes I would like to have a new data type "unique symbol" for constants that are not strings or integers. So we could say "while (EOF !== $value = $reader->read());" but this is another topic) > > johannes