Word Splitter

Splitter.swift

import Foundation

public enum Splitter {
    /// https://stackoverflow.com/a/62527131
    private static let wordBoundaries = #"([^\p{L}\d]+|(?<=\p{L})(?=\d)|(?<=\d)(?=\p{L})|(?<=[\p{Ll}\d])(?=\p{Lu})|(?<=\p{Lu})(?=\p{Lu}\p{Ll})|(?<=[\p{L}\d])(?=\p{Lu}\p{Ll}))"#
    
    static func split(_ string: String) -> AsyncStream<String> {
        AsyncStream<String> { continuation in
            string
                .enumerateSubstrings(in: string.startIndex..., options: .byWords) { (substring, _, _, _) in
                    guard let substring = substring else {
                        return
                    }
                    substring
                        .replacingOccurrences(of: Self.wordBoundaries, with: " ",
                                              options: .regularExpression,
                                              range: substring.startIndex..<substring.endIndex)
                        .split(separator: " ")
                        .forEach { word in
                            continuation.yield(String(word))
                        }
                }
            continuation.finish()
        }
    }
}

SplitterTests.swift

import XCTest
@testable import Splitter

final class SplitterTests: XCTestCase {
    /// https://stackoverflow.com/questions/18379254/regex-to-split-camel-case
    let cases = [
        "MyCamelCaseString": ["My", "Camel", "Case", "String"],
        "ExampleID": ["Example", "ID"],
        "ExampleId": ["Example", "Id"],
        "MyCamelCaseStringID": ["My", "Camel", "Case", "String", "ID"],
        "myCamelCaseString": ["my", "Camel", "Case", "String"],
        "PDFSplitAndMergeSamples": ["PDF", "Split", "And", "Merge", "Samples"],
        "PDFExtractorSDKSamples": ["PDF", "Extractor", "SDK", "Samples"],
        "PDFRendererSDKSamples": ["PDF", "Renderer", "SDK", "Samples"],
        "BarcodeReaderSDKSamples": ["Barcode", "Reader", "SDK", "Samples"],
        "camelCase": ["camel", "Case"],
        "simple": ["simple"],
        "number1Case2": ["number", "1", "Case", "2"],
        "CamelCaseXYZ": ["Camel", "Case", "XYZ"],
        "ThisIsASlug": ["This", "Is", "A", "Slug"],
        "ABCMyCamelCaseSTR": ["ABC", "My", "Camel", "Case", "STR"],
        "ThereIsWay_too  MuchCGIInFilms These-days": ["There", "Is", "Way", "too", "Much", "CGI", "In", "Films", "These", "days"],
        "UnicodeCanBeCAPITALISEDTooYouKnow": ["Unicode", "Can", "Be", "CAPITALISED", "Too", "You", "Know"],
        "CAPITALLetters at the StartOfAString_work_too": ["CAPITAL", "Letters", "at", "the", "Start", "Of", "A", "String", "work", "too"],
        "As_they_DoAtTheEND": ["As", "they", "Do", "At", "The", "END"],
        "BitteWerfenSie-dieFußballeInDenMüll": ["Bitte", "Werfen", "Sie", "die", "Fußballe", "In", "Den", "Müll"],
        "IchHabeUberGesagtNichtÜber": ["Ich", "Habe", "Uber", "Gesagt", "Nicht", "Über"],
        "2BeOrNot2Be": ["2", "Be", "Or", "Not", "2", "Be"],
        "ICannotBelieveThe100GotRenewed. It-isSOOOOOOBad": ["I", "Cannot", "Believe", "The", "100", "Got", "Renewed", "It", "is", "SOOOOOO", "Bad"],
        "colName": ["col", "Name"],
        "This_Is_A_title": ["This", "Is", "A", "title"],
        "And_How_About_thisOne": ["And", "How", "About", "this", "One"],
        "MaryHadALittleLamb": ["Mary", "Had", "A", "Little", "Lamb"],
        "employeeID": ["employee", "ID"],
        "N B A Finals": ["N", "B", "A", "Finals"],
        "N B A Finals in L A": ["N", "B", "A", "Finals", "in", "L", "A"],
        "I Love L A": ["I", "Love", "L", "A"],
        "今天天气如何": ["今天", "天气", "如何"],
        "我的englishSpeaking不是特别nice": ["我", "的", "english", "Speaking", "不", "是", "特别", "nice"],
    ]
    
    func testExamples() async throws {
        for (input, expected) in cases {
            let actual = await Splitter.split(input).collected()
            XCTAssertEqual(actual, expected)
        }
    }
}

/// https://www.hackingwithswift.com/quick-start/concurrency/how-to-convert-an-asyncsequence-into-a-sequence
extension AsyncSequence {
    func collected() async rethrows -> [Element] {
        try await reduce(into: [Element]()) { $0.append($1) }
    }
}