Parse: Use-case based on swift-parsing

swift

import XCTest
import Parsing // https://github.com/pointfreeco/swift-parsing

struct ParsedData {
    let key1: Int
    let key2: UUID?
    let key3: String
}

let parser = Parse(input: Substring.self) {

    /* first line */
    "Key1: "
    Int.parser()
    Whitespace(1, .vertical)

    /* second line */
    Optionally {
        "Key2: "
        Optionally {
            UUID.parser()
        }
        Whitespace(1, .vertical)
    }
    /* third line */
    "Key3: "
    Prefix { $0 != "\n" }.map(.string)
}

let inputVariant1 = """
    Key1: 100
    Key2: AF4D13D7-26C8-41E2-9CB8-AC03CE827921
    Key3: iphone
    """

let inputVariant2 = """
    Key1: 100
    Key2:
    Key3: iphone
    """

let inputVariant3 = """
    Key1: 100
    Key3: iphone
    """

final class Experiment: XCTestCase {
    func testExample() throws {
        do {
            let parsedVariant1 = try parser.parse(inputVariant1) //✅
                print(parsedVariant1)

            let parsedVariant2 = try parser.parse(inputVariant2) //❌
                print(parsedVariant2)

            let parsedVariant3 = try parser.parse(inputVariant3) //✅
                print(parsedVariant3)
        } catch {
            print(error)
        }
    }
}