Unicode::DisplayWidth

Determines the monospace display width of a string in Ruby. Useful for all kinds of terminal-based applications. Implementation based on EastAsianWidth.txt and other data, 100% in Ruby. It does not rely on the OS vendor (like wcwidth()) to provide an up-to-date method for measuring string width.

Unicode version: 16.0.0 (September 2024)

Supported Rubies: 3.3, 3.2, 3.1, 3.0

Old Rubies which might still work: 2.7, 2.6, 2.5, 2.4, 2.3

For even older Rubies, use version 2.3.0 of this gem: 2.3, 2.2, 2.1, 2.0, 1.9

Version 2.4.2 — Performance Updates

If you use this gem, you should really upgrade to 2.4.2 or newer. It's often 100x faster, sometimes even 1000x and more!

This is possible because the gem now detects if you use very basic (and common) characters, like ASCII characters. Furthermore, the charachter width lookup code has been optimized, so even when full-width characters are involved, the gem is much faster now.

Version 2.0 — Breaking Changes

Some features of this library were marked deprecated for a long time and have been removed with Version 2.0:

• Aliases of display_width (…_size, …_length) have been removed
• Auto-loading of string core extension has been removed:

If you are relying on the String#display_width string extension to be automatically loaded (old behavior), please load it explicitly now:

require "unicode/display_width/string_ext"

You could also change your Gemfile line to achieve this:

gem "unicode-display_width", require: "unicode/display_width/string_ext"

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 which 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}", "\u{D7B0}".."\u{D7FF}"	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

Classic API

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, "\t".ord => 10)) # => tab counted as 10, so result is 12

Please note that using overwrites disables some perfomance optimizations of this gem.

Emoji Support

Emoji width support is included, but in must be activated manually. It will adjust the string's size for modifier and zero-width joiner sequences. You also need to add the unicode-emoji gem to your Gemfile:

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

Enable 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

require 'unicode/display_width/string_ext'

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

Modern API: Keyword-arguments Based Config Object

Version 2.0 introduces a keyword-argument based API, which allows you to save your configuration for later-reuse. This requires an extra line of code, but has the advantage that you'll need to define your string-width options only once:

require 'unicode/display_width'

display_width = Unicode::DisplayWidth.new(
  # ambiguous: 1,
  overwrite: { "A".ord => 100 },
  emoji: true,
)

display_width.of "⚀" # => 1
display_width.of "🤾🏽‍♀️" # => 2
display_width.of "A" # => 100

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
• Golang: https://github.com/rivo/uniseg

See unicode-x for more Unicode related micro libraries.

Copyright & Info

• Copyright (c) 2011, 2015-2024 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