How to determine PresentationDetent type in SwiftUI (pre-iOS 16.4).

seriously.swift

extension PresentationDetent {
    /// Converts a `PresentationDetent` to an `ExpandableSheetDetent`
    /// NOTE: Detents created using `.custom(_)` will fail to convert.
    var expandableSheetDetent: ExpandableSheetDetent {
        if self == .medium { return .medium }
        if self == .large { return .large }
        if let height = heightValue { return .height(height) }
        if let fraction = fractionValue { return .fraction(fraction) }
​
        let unknownType = type(of: self)
        fatalError("cannot convert \(unknownType) to ExpandableSheetDetent")
    }
​
    /// Derived height value for a detent created with `.height` case.
    var heightValue: CGFloat? { extractValueFromDescription(key: "height") }
​
    /// Derived fraction value for a detent created with `.fraction` case.
    var fractionValue: CGFloat? { extractValueFromDescription(key: "fraction") }
​
    /// Extracts a value from the description of a detent created with `.height` or `.fraction` cases. Yes,
    /// this is seriously the only way to do this pre-iOS 16.4 release. I'm sorry.
    ///
    /// Assumption the description is formatted like so:
    /// ```
    /// "PresentationDetent(id: SwiftUI.PresentationDetent.Identifier.fraction(0.6))"
    /// // or
    /// "PresentationDetent(id: SwiftUI.PresentationDetent.Identifier.height(50))"
    /// ```
    ///
    /// - Parameter key: The key to extract the value for
    /// - Returns: The extracted value
    private func extractValueFromDescription(key _: String) -> CGFloat? {
        let desc = "\(self)"
        /// Look for numbers (fp or integers) that will be in the description string
        /// The description prints out in canonical format, with the bit we are interested in looking like so:
        /// `<large|medium|fraction(0.5)|height(100)>`
        let pattern = #"[\d.]+(?=\))"#
        guard
            let regex = try? Regex(pattern),
            let match = try? regex.firstMatch(in: desc),
            let doubleValue = Double(match.first?.substring ?? "")
        else { return nil }
​
        return CGFloat(doubleValue)
    }
}