geocoding.rb

class Configuration
  def self.geocoder_service_fallback_order
    [:bing, :google]
  end

  def self.geocoder_default_api
    :bing
  end
end

class Logger
  def self.warn(string)
    puts string
  end
end

class Rails
  def self.configuration
    Configuration
  end

  def self.logger
    Logger
  end
end

class Geocoder
  def self.configure(options)
    puts "Geocoder reconfigured: #{options}"
  end
end

class Geocoder::ServiceUnavailable < Exception; end
class Geocoder::OverQueryLimitError < Exception; end

class SafeGeocoder
  # Public: Takes a block containing a Geocoder method and retries it against
  # fallback services if the block throws Geocoder::ServiceUnavailable
  def self.wrap(&block)
    Rails.configuration.geocoder_service_fallback_order.each do |service|
      Geocoder.configure(lookup: service)
      begin
        return block.call
      rescue Geocoder::ServiceUnavailable, Geocoder::OverQueryLimitError => e
        Rails.logger.warn "#{service} geocoder failed #{e.to_s}"
        next
      end
      break
    end
  ensure
    Geocoder.configure(lookup: Rails.configuration.geocoder_default_api)
  end
end

puts '--- Success ---'
puts SafeGeocoder.wrap {
  "I'm a winner!"
}.inspect
puts
puts '--- Failure ---'
puts SafeGeocoder.wrap {
  raise Geocoder::ServiceUnavailable
}.inspect

output

><((°> ruby temp.rb
--- Success ---
Geocoder reconfigured: {:lookup=>:bing}
Geocoder reconfigured: {:lookup=>:bing}
"I'm a winner!"

--- Failure ---
Geocoder reconfigured: {:lookup=>:bing}
bing geocoder failed Geocoder::ServiceUnavailable
Geocoder reconfigured: {:lookup=>:google}
google geocoder failed Geocoder::ServiceUnavailable
Geocoder reconfigured: {:lookup=>:bing}
[:bing, :google]

Minimal version:

def fallback(&block)
  fallbacks = [:foo, :bar]
  fallbacks.each do |item|
    begin
      return block.call
    rescue
      puts "There was an error. Try next fallback"
      next
    end
    break
  end
end

puts fallback {
  "I'm a winner!"
}.inspect
puts '--'
puts fallback {
  raise 'Oops'
}.inspect

Output:

"I'm a winner!"
--
There was an error. Try next fallback
There was an error. Try next fallback
[:foo, :bar]