StringReplacer

This is a very simple gem that uses regex to replace a string with handlebars notation. A simple use case can be to safely allow a user to define a string that can with a predefined set of avaiable methods that can also take some arguments.

There are other more robust solutions like https://github.com/Shopify/liquid, but if your are looking for a very lightweight extendible solution, this might be the way to go.

Installation

Add this line to your application's Gemfile:

gem 'string_replacer'

And then execute:

bundle

Or install it yourself as:

gem install string_replacer

Usage

The idea is to simple extend the base StringReplacer::Replacer class and user the register_helper class method to define a whitelist of methods you want to have available.

An example:

class CustomStringReplacer < StringReplacer::Replacer
  register_helper(:i18n) do |argument|
    I18n.t(argument.strip)
  end
  
  register_helper(:upcase) do |argument|
    argument.upcase
  end
end

replacer = CustomStringReplacer.new('The {{upcase(translation)}} of hello is: {{i18n(hello)}}')

replacer.replace
# returns 'The TRANSLATION of hello is: hola'

You can even nest multiple methods like this.

replacer = CustomStringReplacer.new('The translation of hello is: {{upcase(i18n(hello))}}')

replacer.replace
# returns 'The translation of hello is: HOLA'

Errors

If there are any errors (like definining a method inside the handlebars that is not registered) execution of the replacement is halted and the errors can be accessed via de errors method.

replacer = CustomStringReplacer.new('This will cause an {{upcase(error)}} {{some_unregisered_method()}}')
replacer.replace
# returns 'This will cause an ERROR {{some_unregisered_method()}}'

replacer.errors
# returns [#<NoMethodError: Unregistered helper 'some_unregisered_method' while interpolating '{{some_unregisered_method()}}'>]

If you want errors to be raised, simply use replace!

Hash arguments

It is possible to pass a hash of arguments that can be accessed by the registered methods. This is helpful when you need some context that is not provided by the handlebars expression.

class AnotherStringReplacer < StringReplacer::Replacer
  register_helper(:current_username) do
    @passed_data[:user_name]
  end
end

replacer = AnotherStringReplacer.new('The name of the current user name is: {{current_username()}}!')
replacer.replace({user_name: 'Yoda'})
# returns 'The name of the current user name is: Yoda!'