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Automatic detection of text direction (ltr, rtl or bidi) for strings in Ruby
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README.md

string-direction

string-direction is a ruby library for automatic detection of the direction (left-to-right, right-to-left or bi-directional) in which a text should be displayed.

Overview

require 'string-direction'

detector = StringDirection::Detector.new

detector.direction('english') #=> 'ltr'
detector.direction('العربية') #=> 'rtl'
detector.direction("english العربية") #=> 'bidi'

detector.ltr?('english') #=> true
detector.rtl?('العربية') #=> true
detector.bidi?('english') #=> false

But, if you prefer, you can monkey patch String:

String.send(:include, StringDirection::StringMethods)

'english'.direction #=> 'ltr'
'العربية'.rtl? #=> true

Strategies

string-direction uses different strategies in order to try to detect the direction of a string. The detector uses them once at a time and returns the result once one of them succeeds, aborting any further analysis.

Strategies are passed to the detector during its initialization:

detector = StringDirection::Detector.new(:foo, :bar)

In the above example, classes StringDirection::FooStrategy and StringDirection::BarStrategy have to be in the load path.

Three strategies are natively integrated: marks, characters & dominant. marks && characters are used as default strategies if no arguments are given to the detector.

marks

Looks for the presence of Unicode direction marks: left-to-right (\u200e) or right-to-left (\u200f).

detector = StringDirection::Detector.new(:marks)

detector.direction("\u200eالعربية") #=> "ltr"
detector.direction("\u200fEnglish") #=> "rtl"

marks strategy can not only analyze a string but everything responding to to_s.

characters

Looks for the presence of right-to-left characters in the scripts used in the string.

By default, string-direction consider following scripts to have a right-to-left writing:

  • Arabic
  • Hebrew
  • Nko
  • Kharoshthi
  • Phoenician
  • Syriac
  • Thaana
  • Tifinagh
detector = StringDirection::Detector.new(:characters)

detector.direction('english') #=> 'ltr'
detector.direction('العربية') #=> 'rtl'

You can change these defaults:

detector.direction('ᚪᚫᚬᚭᚮᚯ') #=> 'ltr'

StringDirection.configure do |config|
  config.rtl_scripts << 'Runic'
end

detector.direction('ᚪᚫᚬᚭᚮᚯ') #=> 'rtl'

This can be useful, mainly, for scripts that have both left-to-right and right-to-left representations:

  • Bopomofo
  • Carian
  • Cypriot
  • Lydian
  • Old_Italic
  • Runic
  • Ugaritic

Keep in mind than only scripts recognized by Ruby regular expressions are allowed.

characters strategy can not only analyze a string but everything responding to to_s.

dominant

With dominant strategy, a string can be left-to-right or right-to-left, but never bidi. It returns one or the other in function of which one has more characters.

detector = StringDirection::Detector.new(:dominant)

detector.direction('e العربية') #=> 'rtl'
detector.direction('english ة') #=> 'ltr'

As with characters strategy, you can change which scripts are considered right-to-left.

dominant strategy can not only analyze a string but everything responding to to_s.

Custom Strategies

You can define your custom strategies. To do so, you just have to define a class inside StringDirection module with a name ending with Strategy. This class has to respond to an instance method run which takes the string as argument. You can inherit from StringDirection::Strategy to have convenient methods ltr, rtl and bidi which return expected result. If the strategy doesn't know the direction, it must return nil.

class StringDirection::AlwaysLtrStrategy < StringDirection::Strategy
  def run(string)
    ltr
  end
end

detector = StringDirection::Detector.new(:always_ltr)
detector.direction('العربية') #=> 'ltr'

Changing default strategies

marks and characters are default strategies, but you can change them:

StringDirection.configure do |config|
  config.default_strategies = [:custom, :marks, :always_ltr]
end

Monkey patching String

If you desire, you can monkey patch String:

String.send(:include, StringDirection::StringMethods)

'english'.direction #=> 'ltr'

In that case, strategies configured in string_method_strategies are used:

StringDirection.configure do |config|
  config.string_methods_strategies = [:marks, :characters]
end

Release Policy

string-direction follows the principles of semantic versioning.

Disclaimer

I'm not an expert neither in World scripts nor in Unicode. So, please, if you know some case where this library is not working as it should be, open an issue and help improve it.

Thanks

Omniglot.com, where I learnt which Ruby recognized scripts have a right-to-left writing system.

LICENSE

Copyright 2013 Marc Busqué - marc@lamarciana.com

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

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