Parsing URL array-formatted parameter

[mergesort]

I'm looking to create a new route for my app, which will take a urls parameter which contains multiple comma-separated values, and parse them into domain-specific objects I can display. An example URL looks something like this:

https://plinky.app/links?urls=https://www.apple.com,https://www.google.com,https://www.microsoft.com

Presumably I can parse the parameter by separating out the comma-separated values like so:

let parsedURLs = urls.split(separator: ",").compactMap { URL(string: String($0)) }

But I was wondering if there was a built-in way/better to do this with Query and Field, that way I don't have to store this case's property as a String?

Thanks a lot!

[mbrandonw]

Hi @mergesort, the second argument of Field is a Conversion, which describes a way of transforming an input to an output and back into an input. It's similar to a parser, but it does not consume anything. It just transforms back-and-forth.

So you can create a custom conversion for turning a string into an array of URLs and back:

struct CommaSeparatedURLs: Conversion {
  func apply(_ input: Substring) throws -> [URL] {
    input.split(separator: ",").compactMap { URL(string: String($0)) }
  }
  func unapply(_ output: [URL]) throws -> Substring {
    output.map(\.absoluteString).joined(separator: ",")[...]
  }
}

And then you can use this with Field:

Field("links", CommaSeparatedURLs())

And you can also add a static var to Conversion to give a nicer syntax if you want.

[mergesort]

Thank you so much for the idea and the prompt reply @mbrandonw! I had taken a look before to see if I could recreate what y'all do with .string, Digits(), etc, but hadn't figured it out. This is so simple that I'm now going to apply this technique to a few other places I've resorted to saving string-representations.

Unless I missed it I don't believe I saw this documented anywhere, if not it's definitely worth adding somewhere people can find. 😄

Thanks again!