range-v3 VS RE2

std::ranges is in c++20, but you can pull in the library it was based on if you use 17 (https://github.com/ericniebler/range-v3)

What you are describing seems to be std::ranges. If you’re interested in understanding how to implement it, I recommend checking out the original reference implementation, rangev3. Trying to implement your own ranges framework is really good practice for learning how to do efficient, advanced generic programming in C++. I highly recommend it as a hobby learning project. But it’s also really, really hard to do correctly, so please just use the stdlib and/or rangev3 in any real project.

In C++23, there will be std::views::cartesian_product. It is already available in the range-v3 library, the one that the standard is based on.

/** * @brief Forwards value equivalent to the std::forward. * * Using cast instead of std::forward to avoid template instantiation. Used by * Eric Niebler in range library. * * @see https://github.com/ericniebler/range-v3 */

It uses a custom zip_iterator (which isn't very good, and you should really use the one from boost or from range-v3).

It contains very little functionality compared to the Eric Niebler’s reference implementation for my liking. Especially views. This will undoubtedly change in the future. But the point is moot, because they are not really supported the is no other option for now other than https://github.com/ericniebler/range-v3.

range-v3 is a great library allowing you to bridge the gap: https://github.com/ericniebler/range-v3

[range-v3](https://github.com/ericniebler/range-v3) which std::ranges was based on has the `to>()` which as far as I know is expected to get into c++23 :)

Looking at the benchmark where C++ is worst compared to other languages, it's depending on the library used. I would guess if they used Google's re2 Regex library instead of Boost's, the result would be different.

https://github.com/google/re2

https://github.com/greensoftwarelab/Energy-Languages/blob/ma...

That page says it just includes "some of the most common special characters", and following the link to the Examples page in turn includes a link to the full list.

Python uses backtracking, so this probably isn't O(n), especially with the ability to choose the dictionary.

But with there are non-backtracking matchers which would make this O(n). Here's re2 from https://github.com/google/re2 :

  >>> import re2

RE2 is a Google regular expression library

google's regex library: https://github.com/google/re2

I am currently working with Regex, specifically Re2, and was wondering if there is a real difference between the above expressions for repeated sub-regex.

I ported Google RE2, a regular expression library, to SPVM as Resource::Re2, and created SPVM::Regex, a wrapper for it.

I searched for I found that there is a Perl compatible regular expression called Google RE2. It is written in C++, and with Google RE2, I can use Perl-compatible regular expressions as a library.

Yes, but there is an interesting clarification here. RE2 has used the "caching" approach documented in the Ruby bug ticket linked for quite some time (since its birth?): https://github.com/google/re2/blob/954656f47fe8fb505d4818da1...

It is mentioned only briefly in Cox's article on regex matching in the wild. Look for the word "bitstate": https://swtch.com/~rsc/regexp/regexp3.html

I didn't know Perl had implemented this trick too.

The paper[1] cited in the Ruby bug ticket was published very recently. When I first read the Ruby bug ticket, I immediately wondered how they sidestepped the memory use problem. The paper's abstract seems to suggest there is some technique for doing so, as it rebuffs the idea of doing "full" memoization. Alas, I do not have access the paper. (Which is fucking ridiculous.)

[1]: https://ieeexplore.ieee.org/abstract/document/9519427