EastAsianWidth

Extension of Swift String API to deal with East Asian Width. The most generally use case is to classify unicode scalar value as Fullwidth (全角) or Halfwidth (半角).

// Halfwidth Katakana (半角カナ)
"ｱｲｳｴｵ".unicodeScalars.forEach { (u: UnicodeScalar) in
    u.isHalfwidth // true
}

// Fullwidth Katakana (全角カナ)
"アイウエオ".unicodeScalars.forEach { (u: UnicodeScalar) in
    u.isFullwidth // true
}

East Asian Width is specified as Unicode® Standard Annex #11.

Usage

UnicodeScalar Extensions

For East Asian Width, this library provides methods below

/// East Asian Wide (W)
/// See: http://unicode.org/reports/tr11/#ED4
unicodeScalar.isEastAsianWide

/// East Asian Narrow (Na)
/// See: http://unicode.org/reports/tr11/#ED5
unicodeScalar.isEastAsianNarrow

/// Neutral (Not East Asian):
/// See: http://unicode.org/reports/tr11/#ED7
unicodeScalar.isEastAsianNeutral
        
/// East Asian Halfwidth (H)
/// See: http://unicode.org/reports/tr11/#ED3
unicodeScalar.isEastAsianHalfwidth

/// East Asian Fullwidth (F)
/// See: http://unicode.org/reports/tr11/#ED2
unicodeScalar.isEastAsianFullwidth
        
/// East Asian Ambiguous (A)
/// See: http://unicode.org/reports/tr11/#ED6
unicodeScalar.isEastAsianAmbiguous

And if you want to know just it is Fullwidth(全角) or Halfwidth(半角), you can use isFullwidth and so on.

// Fullwidth
unicodeScalar.isFullwidth

// Halfwidth
unicodeScalar.isHalfwidth

// NOTE:
// `isFullwidth` and `isHalfwidth` does not include East Asian Ambiguous.
// If you want to include it, you can use `isFullwidthOrAmbiguous` / `isHalfwidthOrAmbiguous` instead.
unicodeScalar.isFullwidthOrAmbiguous
unicodeScalar.isHalfwidthOrAmbiguous

String Extensions

String extension provides containsXXX methods that check if specific East Asian Width characters are contained.

// East Asian Width
string.containsEastAsianWideCharacters
string.containsEastAsianNarrowCharacters
string.containsEastAsianNeutralCharacters
string.containsEastAsianHalfwidthCharacters
string.containsEastAsianFullwidthCharacters
string.containsEastAsianAmbiguousCharacters

// Fullwidth or Halfwidth
string.containsFullwidthCharacters
string.containsFullwidthOrAmbiguousCharacters
string.containsHalfwidthCharacters
string.containsHalfwidthOrAmbiguousCharacters

UnicodeScalarView Extensions

UnicodeScalarView extension provides countByEastAsianWidth method that counts string length by East Asian Width.

By default, Ambiguous characters are marked as Halfwidth, length of Halfwidth is 1, and Fullwidth is 2. You can configure them with parameters.

// count by defualt settings
"あいうえおｱｲｳｴｵ".unicodeScalars.countByEastAsianWidth() // 15

// you can configure with parameters.
string.unicodeScalars.countByEastAsianWidth(halfwidthAs: 2, fullwidthAs: 4, markEastAsianAmbiguousAsFullwidth: false)

Why not support CharacterSet ?

Main reason is technical problems of CharacterSet. We cannot create union of CharacterSet that has different byte length characters.

let c1 = CharacterSet(charactersIn: "\u{AAAA}")
let c2 = CharacterSet(charactersIn: "\u{AAAAA}")

c2.contains("\u{AAAAA}") // true
c1.union(c2).contains("\u{AAAAA}") // false 😫

But some East Asian Width definitions include different byte length characters. So I cannot support CharacterSet…

Requirements

EastAsianWidth.swift requires / supports the following environments:

• Swift 4 / Xcode9
• OS X 10.10 or later
• iOS 9.0 or later
• tvOS 9.0 or later
• watchOS 2.0 or later