Hi Sunday, June 6, 2004, 10:32:10 PM, you wrote: [snip]
I don't propose to narrow implementation only to std::string. My point is:
String algorithm always take string as a whole. And if I do not want it, there should not be single ::iterator or .begin() assumed by interface to be used by user.
I don't know if I understand you correctly. User will almost never be forced to use .begin(). Collection traits are incorporated in the whole lib, so .begin() and etc. is used automaticaly, depending on the type of the collection. ::iterator is used only once in the defintion of the find_iterator type. It it only a single typedef, that user has to use. There are more options then char or wchar_t, and it is up to the user to decide. For instance, you can iterate over const_iterator of mutable iterator. That's the reason why these typedef are not part of the library. If it would be requested, I can include most common ones.
And for the iterator range: it provides a reference into the original string. It if most efficient way to doing so, because you don't pay anything if you want just read the content there. For other operation you can simply use boost::copy_iterator_range, to extract the match to your favorite container.
I agree that we need something to efficiently model substring. IMO something like basic_cstring is better choice for use with string algorithms. It may be less generic than iterator_range, but should be generic enough to cover 99% cases.
I have checked your basic_cstring. IMHO it is not usable in the context of the string_algo lib. It is restricted to char* (I definitely need iterators). It bundles algorithms inside a class - this violates the decapulated design policy. I don't realy know what do you have agains iterator_range. It is used only as a reference to the searched input. It is up to the user what will do with this reference. Why whould we want to enforce the user to use something, she does not want to? Can you please be more specific, what features/use-cases are you lacking with the iterator_range approach when compared to basic_cstring?
2. Finder concept maybe useful in implementing different string search algorithm. BUT as implementation detail or generic case solution. I do not see any reason for interface that assumes explicit specification of finders provided by the library. There should be a generic algorithm/iterator that expect User defined finder, but there should be explicit algorithms/iterators dedicated for each type of search. I do that for algorithms, why not for iterators?
They are there actually for most of the algorithms. find/split_iterator is quite new stuff. Originally it has been encapsulated by find_all and split algorithms (they are still there, see split.hpp). During the review it has been expressed, that pure iterator-base interface is better for split operations. Therefore I have refactored the implementation so it can be used directly.
IMO to be convenient you should've split iterators on many as you did with algorithms. Also you can keep generic find_iterator for use with custom finder.
I will do this. Actualy it is not needed to specify a class for every type of iterator. Just a constructor functions.
find_iterator is also based on generic iterator concept, however, the iterator is the only template parameter, so you can easily specialize for string.
Simple usage looks like this:
In fact from your sources it seems that I have to write like this
boost::split_iterator<std::string::iterator> it( str.begin(), str.end(), boost::token_finder(boost::is_any_of(";,"));
IMO it's way to verbose, while still missing some of the functionality provided by the tokenizer library.
Actually you have missed the important constructor. You can write:
boost::split_iterator<std::string::iterator> it( str, boost::token_finder(boost::is_any_of(";,"));
str will be expanded automatically. And you can also use char*, wchar_t of vector<char>.
Did I? Could you point on file:line?
I'm sorry, I'm starting to have a little mess. I forgot, that I haven't commited the latest update. It is there now.
Even this is too much IMO. There should not be ::iterator. I prefer boost::basic_split_iterator<char> ( = split_iterator ).
And how do you distinguish between "const_iterator" and "iterator" ? And how can you distinguish between iteration over vector<char>, rope<char> or basic_string<char>. Or even (with a little adaptation in collection_traits) CString?
My choice:
boost::token_iterator it( str, boost::dropped_delimiters = ";," );
It is very easy to implement forwarder to this kind of syntax. As I said, find_iterator is relatively new, so I have extended the interface to full extend yet. I will keep this in mind. Thanks for idea.
It should be separate class for every predefined finder IMO. Also keep in mind that boost::tokenizer provide additional functionality that is not covered by above finder.
I didn't mean to mimic tokenizer. Although I will try to incorporate as much of its functionality as possible. As I have written above, there is not a need for a separate class for every type of finder.
Second concern about your solution, that makes it in a sense even worse than the one provided by boost::tokenizer, is that you actually does not specify type of the Finder in the iterator specification. The price is that eventually you have to, this way or another, pay with runtime overhead. This would be unacceptable to me.
This is a design point. First implementation had templated specification of the finder. However, the usage of such a class was very inconvenient due to complicated specification. Therefore it was changed to the current state. The runtime overhead implied by the current implementation is rather small. I actually only adds one indirection in the increment operation. So it is neglible.
You had to make this decision namely because you are trying to pull several independent (though similar) algorithms under the same interface hood and do not want burden of explicit type Finder type specification. But what is so common among these iterators to do so? On the other hand, in many cases all that the increment does is a couple comparisons. There is chance it could be inlined. Now you need to pay for function invocation.
You might have a look into the implementation. There is realy only one additional dereference per increment. Finding operation is usualy at least O(n), so one far jmp does not bring any degradation in performance. find_iterator needs to consult the finder only there. Local state is stored directly in the iterator so comparisons and dereference have no additional overhead.
There are couple of things that your solution provide in addition to what my and boost::tokenizer solution provide. Particularly it's an ability to specify several addition delimitation policies. I thought about this. But it isn't on top of my priorities (mostly because it is comparatively rarely needed). In any case this generic solution should not interfere with most convenient one used in majority of the cases.
Rationale in find_iterator is quite simple. There is a well defined concept of Finder in the lib and there is also a bunch of finders already implemented there. find_iterator is a natural candidate to use this facility.
I don't mind find_iterator by itself. But there should be separate token_iterator with different tradeoffs: It more specific (less flexible), but more convenient and efficient.
Maybe thats the direction where boost::tokenizer should head. find_iterator is an extension to Finder. If you have a bunch of finders, it provides a useful functionality. However, I'd like to offer as much of usablity and convenience as possible. Regards, Pavol