Below is my review of the proposed Boost.Parser.
## What is your evaluation of the design?
I thought it was easier to pick-up and use than Spirit. How to use the library is clear, and I didn't see any real gotchas floating around. Like others I appreciate that the library has a descriptive name.
## What is your evaluation of the implementation?
It's generally pretty clean. The numeric parsing in seems to be a reduced version of the parser from Spirit X3. To test if it was similar I ran this library through the Boost.Charconv benchmarks for performance evaluation with parsing floats, doubles, uint32, and uint64. I ran this using Homebrew GCC 13.2.0 on an M1 Mac. The test set consists of a test set of 2'000'000 random numbers of each type, and that test set is run 5 times. The timing in the left column is the average time to parse 1 number (i.e. total time / 10'000'000).
----from_chars float----
29.7 ns | std::strtof float scientific
36.7 ns | std::strtod double scientific
519.9 ns | Boost.lexical_cast float scientific
574.0 ns | Boost.lexical_cast double scientific
28.3 ns | Boost.Spirit.Qi float scientific
34.7 ns | Boost.Spirit.Qi double scientific
72.1 ns | Boost.Parser float scientific
78.9 ns | Boost.Parser double scientific
22.0 ns | std::from_chars float scientific
22.2 ns | std::from_chars double scientific
23.0 ns | Boost.Charconv::from_chars float scientific
22.7 ns | Boost.Charconv::from_chars double scientific
65.6 ns | Google double-conversion float scientific
115.2 ns | Google double-conversion double scientific
-----from_chars int-----
23.1 ns | std::strtoul uint32_t
26.8 ns | std::strtoull uint64_t
40.4 ns | Boost.lexical_cast uint32_t
51.4 ns | Boost.lexical_cast uint64_t
29.3 ns | Boost.Spirit.Qi uint32_t
29.4 ns | Boost.Spirit.Qi uint64_t
53.7 ns | Boost.Parser uint32_t
66.3 ns | Boost.Parser uint64_t
11.1 ns | std::from_chars uint32_t
16.4 ns | std::from_chars uint64_t
10.0 ns | Boost.Charconv::from_chars uint32_t
16.3 ns | Boost.Charconv::from_chars uint64_t
The library requires C++17 so it may be worth offloading some of the numeric cases to <charconv> if possible.
The only thing I didn't like seems to be a carry-over from Spirit. Most numeric types have a parser of the form type_ (e.g. float_, int_, etc). ulong_long and long_long are both missing the trailing underscore which is a small enough difference to be surprising and a bit annoying.
I think the CI could be more comprehensive. All of the current testing is run on x86_64. The boost drone has ARM Mac, S390X, and aarch64 all running natively. Boost.CI also has some docker images of other architectures. I concur with Chris about adding CodeCov to the CI. I have added it to a number of boost libraries recently, and it has helped us to find, and fix dark corners of the codebase.
## What is your evaluation of the documentation?
It was well written. I appreciate that it's example driven instead of a pure wall of text. You can clearly do a lot with the library and it leads you into depth at an adequate pace.
## What is your evaluation of the potential usefulness of the library?
The potential usefulness is high. Having a solid and modern parser in boost fills a need that I am sure most of us will have throughout our careers.
## Did you try to use the library? With what compiler? Did you have any problems?
Yes. I ran everything on an M1 Mac with Homebrew GCC 13.2.0. The only real problem I had was with CMake, and I opened an issue against the library here: https://github.com/tzlaine/parser/pull/98
## How much effort did you put into your evaluation? A glance? A quick reading? In-depth study?
I spent time on and off this week. Read the docs, read through the code, wrote the test program, and opened a PR for an issue I had with CMake as mentioned above.
## Are you knowledgeable about the problem domain?
My domain knowledge is more specific to numerical parsing than general purpose like other reviewers.
## Do you think the library should be accepted as a Boost library?
Yes without condition. Thanks for writing this Zach. Based off the git history it has been a long time coming.
## Disclosure
I am a staff engineer with the C++ Alliance.
Matt
