Generic Reference type and match result subscript

[rxwei]

Change Reference to generic type over Capture. Add a subscript<T>(_: Reference<T>) -> T to RegexMatch to allow the user to access a capture via a reference.

Alternatives considered:

• subscript(_: Reference) -> Any with non-generic Reference. While creating a Reference would remain easy, it would lose the benefits of strong types.
• Reference<Capture>.init() where Capture == Substring. This allows writing Reference() to conveniently create a Reference<Substring>, but when it’s used on any transformed capture, it causes the “expression is too complex” error. I think this is a harmful outcome as it's hard for developers to figure that the fix is actually specifying a type in the Reference initializer.

---

Examples:

let a = Reference(Int.self)
let result = regex.match {
  tryCapture(as: a) {
    oneOrMore(.digit)
  } transform: { Int($0) }
}
result[a] // => Int

[rxwei]

@swift-ci please test Linux

[natecook1000]

Now that we've flattened the structured capture groups, can the capture(_:as:) method capture anything other than a Substring? I'm not sure the generic parameter is required in the non-transforming overload. Without that, we should be able to revert to the optional/nil default approach, which cuts the number of overloads in half. Edit: Oh, surely a RegexComponent type that provides a different type would do that…

[rxwei]

Yes, the new capture type produced by capture and tryCapture is the whole match type of the component.

[milseman]

LGTM

[milseman]

IIUC, this will (eventually) allow our storage form to be purely range based.

[rxwei]

This is now purely range based.

[rxwei]

@swift-ci please test

[rxwei]

@swift-ci please test