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/*
This source file is part of the Swift.org open source project
Copyright (c) 2024 Apple Inc. and the Swift project authors
Licensed under Apache License v2.0 with Runtime Library Exception
See https://swift.org/LICENSE.txt for license information
See https://swift.org/CONTRIBUTORS.txt for Swift project authors
*/
import Foundation
extension String {
// Precomputes the CharacterSet to use in capitalizingFirstWord().
private static let charactersPreventingWordCapitalization = CharacterSet.lowercaseLetters.union(.punctuationCharacters).inverted
/// Returns the string with the first letter capitalized.
/// This auto-capitalization only occurs if the first word is all lowercase and contains only lowercase letters.
/// The first word can also contain punctuation (e.g. a period, comma, hyphen, semi-colon, colon).
func capitalizingFirstWord() -> String {
guard let firstWordStartIndex = self.firstIndex(where: { !$0.isWhitespace && !$0.isNewline }) else { return self }
let firstWord = self[firstWordStartIndex...].prefix(while: { !$0.isWhitespace && !$0.isNewline})
guard firstWord.rangeOfCharacter(from: Self.charactersPreventingWordCapitalization) == nil else {
return self
}
var resultString = self
resultString.replaceSubrange(firstWordStartIndex..<firstWord.endIndex, with: firstWord.localizedCapitalized)
return resultString
}
}
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