Case Insensitive String Matching

new_method.rb

# Create a new predicate method
#
# Eg., 'ABC'.similar?('abc') # true
#
# Pros: Simple. Intention-revealing.
# Cons: No sugar.

module CoreExtensions
  module String
    def similar?(value)
      casecmp(value).zero?
    end
  end
end

String.prepend(CoreExtensions::String)

new_operator.rb

# Create a new operator by combining a binary & unary operator
#
# Eg., 'ABC' ==~ 'abc' && 'ABC' !=~ 'def' # true
#
# Pros: Syntactic sugar. Allows overloading the == and != operators.
# Cons: Rubocop complains about the lack of space between operators.

module CoreExtensions
  module String
    def ~
      @complemented = !@complemented
    end
    
    def complemented?
      @complemented
    end
    
    def ==(value)
      if value.respond_to?(:complemented?) && value.complemented?
        ~value # uncomplement value
        casecmp(value).zero?
      else
        super
      end
    end
    
    def !=(value)
      if value.respond_to?(:complemented?) && value.complemented?
        ~value # uncomplement value
        !casecmp(value).zero?
      else
        super
      end
    end
  end
end

String.prepend(CoreExtensions::String)

overloaded_operator.rb

# Overload an existing operator
#
# Eg., 'ABC' =~ 'abc' # true
#
# Pros: Syntactic sugar. Stylistically correct according to Rubocop.
# Cons: Could be unintuitive to rubyists unaware of our core extensions.
#       Unable to define !=~.

module CoreExtensions
  module String
    def =~(value)
      if value.is_a?(String)
        casecmp(value).zero?
      else
        super
      end
    end
  end
end

String.prepend(CoreExtensions::String)