Look at if a generated regex parser can do better job than pugixml (performance wise)

[mithro]

pugixml is a generic XML parser. However, now we are generating a parser, we should see if we can do better by creating a parser that only parses files in the exact given XML formats. Using something like Google's re2 would be a good option for that.

[mithro]

See also https://rust-leipzig.github.io/regex/2017/03/28/comparison-of-regex-engines/ and https://news.ycombinator.com/item?id=14608663

[duck2]

I don't think this would work. Even the non-requirement of order on the attributes will make the resulting regular expression explode combinatorially. Think of an element with 6 required attributes:

<element (attr1="([\w]*)" attr2="([\w]*)" attr3="([\w]*)" attr4="([\w]*)" attr5="([\w]*)" attr6="([\w]*)")
|(attr1="([\w]*)" attr2="([\w]*)" attr3="([\w]*)" attr4="([\w]*)" attr6="([\w]*)" attr5="([\w]*)"
| [718 more permutations...] >

[mithro]

Use an or and a match X times. Something like....

<element (attr1="([\w]*)"|attr2="([\w]*)"|attr3="([\w]*)")*>

[duck2]

Yes, but then we won't be checking if all required attributes are present. State machines are really bad at handling independent inputs.

[mithro]

@duck2 - That can be done after the tag has been parsed?

[duck2]

Need to think more. Maybe we could make something like an opinionated SAX parser out of this, output of which can be fed to the general purpose validators.

[mithro]

@duck2 Notice how I separated some final validation from the parsing in the example here -> https://github.com/duck2/uxsdcxx/issues/1#issuecomment-506573231