Bindings for the ICU library icu internationalization globalization
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Crystal ICU

Crystal binding/wrapper to the ICU library



apt-get install -y libicu-dev


brew install icu4c
brew link --force icu4c


Add this to your application's shard.yml:

    github: olbat/

Then require the lib in your Crystal code:

require "icu"

Wrapped components (WIP)

  • [x] CharsetDetector, Charset detection (ucsdet.h)
  • [x] BreakIterator, Text Boundary Analysis (Break Iteration) (ubrk.h)
  • [x] Transliterator, Text Transformation (Transliteration) (utrans.h)
  • [x] Normalizer, Normalization (unorm2.h)
  • [x] Collator, Collation (ucol.h)
  • [x] StringSearch, String Searching (usearch.h)
  • [x] IDNA, International Domain Names in Applications (uidna.h)
  • [x] Currencies, Encapsulates information about a currency (ucurr.h)
  • [x] Region, Territory containment and mapping (uregion.h)
  • [x] UniversalTimeScale, Universal Time Scale (utmscale.h)
  • [ ] uregex, Regular Expressions (uregex.h)
  • [ ] uloc, Locales (uloc.h, ulocdata.h)
  • [ ] unum, Number Formatting/Spellout (unum.h)
  • [ ] ubidi, Bidirectional Algorithm (ubidi.h)
  • [ ] ucnv, Codepage Conversion (ucnv.h, ucnvsel.h)
  • [ ] ucal, Calendars (ucal.h)
  • [ ] udat, Date and Time Formatting (udat.h, udatpg.h, udateintervalformat.h)
  • [ ] upluralrules, Plural rules (upluralrules.h)


  • [x] UChars, UChar conversion routines
  • [x] UEnum, String Enumeration (uenum.h)
  • [ ] ustring, Strings and Character Iteration (ustring.h, uiter.h)
  • [ ] utext, Abstract Unicode Text API (utext.h)
  • [ ] uset, Sets of Unicode Code Points and Strings (uset.h)
  • [ ] ures, Resource Bundles (ures.h)
  • [ ] usprep, StringPrep (usprep.h)
  • [ ] uspoof, Identifier Spoofing & Confusability (uspoof.h)
  • [ ] udata, Data loading interface (udata.h)


ICU version compatibility

This binding is compatible with the ICU library starting from version 4.8. It has been generated using ICU version 57.1 so every additions in the API from this version will not be present in this binding.

The Crystal wrapper's (the ICU class) class and methods are enabled dynamically at compile-time depending on the version of the ICU library that's installed.

Please make sure that the class/feature you want to use is supported by your version ICU by checking the API documentation.

Regenerate the binding

To be sure that the LibICU binding fits with the version of the lib that's installed, it's possible to regenerate the binding by:

  1. Installing libgen and it's dependencies (cf. libgen's documentation)
  2. Run libgen and the lib_transformer program by running make generate_lib

Project's structure

  • src/lib_icu: this directory contains the binding to the ICU library, it's generated by libgen & a transformation program
  • src/icu: this directory contains the wrapper to the LibICU crystal lib that eases the usage of the binding
  • src/ this small program is used to determine which version of ICU is installed on the system (see #1)
  • src/ this small program is used to fix the binding generated by libgen (see #3)

About the binding's generation

For implementation and technical details about the binding's generation, see #1 & #3.


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request


  • olbat Luc Sarzyniec - creator, maintainer
  github: olbat/
License GPLv3
Crystal >= 0.23.0


Libraries 1

  • libicu: >= 4.8

Dependencies 0

Development Dependencies 1

  • libgen ~> 0.2.11
    {'github' => 'olbat/libgen', 'version' => '~> 0.2.11'}

Dependents 0

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