ifelse_2.rb

# before
module Main
  def self.convert(file, format)
    if format == 'png'
      PngGenerator.generate(file)
    elsif format == 'gif'
      GifGenerator.generate(file)
    elsif format == 'bmp'
      BmpGenerator.generate(file)
    elsif format == 'tiff'
      TiffGenerator.generate(file)
    elsif format == 'pdf'
      PdfGenerator.generate(file)
    end
  end
end

# after
module Main2
  DICTIONARY = {
    'png' => PngGenerator,
    'gif' => GifGenerator,
    'bmp' => BmpGenerator,
    'tiff' => TiffGenerator,
    'pdf' => PdfGenerator
  }.freeze

  def self.convert(file, format)
    DICTIONARY[format].generate(file)
  end
end