Parsing to dictionaries

[JaapWijnen]

Hi! I've been doing some xml related parsing recently and I run into an issue when parsing attributes such as:
<xmlTag "attr1"="value1" "attr2"="value2" />
When parsing these to a dictionary round tripping wil occasionally fail since dictionaries are unordered so the printed order will be reversed for example.
So I switched to swift-collections' OrderedDictionary which fixed the problem.
A few of swift-collections' types don't conform to collection however due to protocol requirement clashes with subscripts I believe.

Specifically the End() parser requires Input to conform to Collection. Summarising I have two questions:

• Are there better ways to get around my ordered dictionary problem with xml/html attributes?
• Could we loosen the restrictions on the End parser to Sequence?

Something like this seems to work in this case:

struct SequenceEnd<Input: Sequence>: Parser {
    func parse(_ input: inout Input) throws {
        var iterator = input.makeIterator()
        guard iterator.next() == nil else {
            throw SomeError()
        }
    }
}

Let me know what you think!

[stephencelis]

Hi @JaapWijnen! I converted this to a discussion since we use issues for bug tracking.

Can you share more of your use case? It sounds like you're parsing a substring/bytes into an OrderedDictionary, so OrderedDictionary would be the output, not the input, right? Or are you trying to write a parser against an ordered dictionary?

[stephencelis]

Makes sense and should be possible with the tools we ship with! If you're having any particular problems, feel free to share what you have so far.

[JaapWijnen]

Yeah it's absolutely possible! I meant to ask would it be possible to drop End parser's Input restriction to Sequence instead of Collection to have better support for the swift-collection package for example. Or do you foresee other problems with that?
(there could be other Parsers/ParserPrinters for which this might be interesting but I haven't run into them yet.

Regarding that ordered dictionary. Would that be the way to go in order to make that roundtrippable? Or would you have a different suggestion? I'd rather use normal ones of course.

[stephencelis]

Yeah it's absolutely possible! I meant to ask would it be possible to drop End parser's Input restriction to Sequence instead of Collection to have better support for the swift-collection package for example.

Oh! That sounds reasonable to me. Wanna try to PR and see if anything comes up?

[JaapWijnen]

Will do!

[JaapWijnen]

Done! #250