Unicode::DisplayWidth

Determines the monospace display width of a string in Ruby. Implementation based on EastAsianWidth.txt and other data, 100% in Ruby. Other than wcwidth(), which fulfills a similar purpose, it does not rely on the OS vendor to provide an up-to-date method for measuring string width.

Unicode version: 13.0.0 (March 2020)

Supported Rubies: 2.7, 2.6, 2.5, 2.4

Old Rubies that might still work: 2.3, 2.2, 2.1, 2.0, 1.9

Introduction to Character Widths

Guessing the correct space a character will consume on terminals is not easy. There is no single standard. Most implementations combine data from East Asian Width, some General Categories, and hand-picked adjustments.

How this Library Handles Widths

Further at the top means higher precedence. Please expect changes to this algorithm with every MINOR version update (the X in 1.X.0)!

Width	Characters	Comment
X	(user defined)	Overwrites any other values
-1	"\b"	Backspace (total width never below 0)
0	"\0", "\x05", "\a", "\n", "\v", "\f", "\r", "\x0E", "\x0F"	C0 control codes that do not change horizontal width
1	"\u{00AD}"	SOFT HYPHEN
2	"\u{2E3A}"	TWO-EM DASH
3	"\u{2E3B}"	THREE-EM DASH
0	General Categories: Mn, Me, Cf (non-arabic)	Excludes ARABIC format characters
0	"\u{1160}".."\u{11FF}"	HANGUL JUNGSEONG
0	"\u{2060}".."\u{206F}", "\u{FFF0}".."\u{FFF8}", "\u{E0000}".."\u{E0FFF}"	Ignorable ranges
2	East Asian Width: F, W	Full-width characters
2	"\u{3400}".."\u{4DBF}", "\u{4E00}".."\u{9FFF}", "\u{F900}".."\u{FAFF}", "\u{20000}".."\u{2FFFD}", "\u{30000}".."\u{3FFFD}"	Full-width ranges
1 or 2	East Asian Width: A	Ambiguous characters, user defined, default: 1
1	All other codepoints	-

Install

Install the gem with:

$ gem install unicode-display_width

Or add to your Gemfile:

gem 'unicode-display_width'

Usage

require 'unicode/display_width'

Unicode::DisplayWidth.of("⚀") # => 1
Unicode::DisplayWidth.of("一") # => 2

Ambiguous Characters

The second parameter defines the value returned by characters defined as ambiguous:

Unicode::DisplayWidth.of("·", 1) # => 1
Unicode::DisplayWidth.of("·", 2) # => 2

Custom Overwrites

You can overwrite how to handle specific code points by passing a hash (or even a proc) as third parameter:

Unicode::DisplayWidth.of("a\tb", 1, 0x09 => 10)) # => 12

Emoji Support

Experimental emoji support is included. It will adjust the string's size for modifier and zero-width joiner sequences. You will need to add the unicode-emoji gem to your Gemfile:

gem 'unicode-display_width'
gem 'unicode-emoji'

You can then activate the emoji string width adjustments by passing emoji: true as fourth parameter:

Unicode::DisplayWidth.of "🤾🏽‍♀️" # => 5
Unicode::DisplayWidth.of "🤾🏽‍♀️", 1, {}, emoji: true # => 2

Usage with String Extension

Activated by default. Will be deactivated in version 2.0:

require 'unicode/display_width/string_ext'

"⚀".display_width #=> 1
'一'.display_width #=> 2

You can actively opt-out from the string extension with: require 'unicode/display_width/no_string_ext'

Usage From the CLI

Use this one-liner to print out display widths for strings from the command-line:

$ gem install unicode-display_width
$ ruby -r unicode/display_width -e 'puts Unicode::DisplayWidth.of $*[0]' -- "一"

Replace "一" with the actual string to measure

Other Implementations & Discussion

• Python: https://github.com/jquast/wcwidth
• JavaScript: https://github.com/mycoboco/wcwidth.js
• C: https://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c
• C for Julia: JuliaStrings/utf8proc#2

See unicode-x for more Unicode related micro libraries.

Copyright & Info

• Copyright (c) 2011, 2015-2020 Jan Lelis, https://janlelis.com, released under the MIT license
• Early versions based on runpaint's unicode-data interface: Copyright (c) 2009 Run Paint Run Run
• Unicode data: https://www.unicode.org/copyright.html#Exhibit1