simple_cache.rb

# Failsafe operation mode
#
# Instantiate the cache with a block. Conditionally store the correct value
# only if the operation succeeds. Future calls to get must provided a fallback
# block, or they will recieve an error

cache = SimpleCache.new expires: 4.hours do |store, from, to|
  begin
    # Don't referesh cache if my_thing fails. An existing previous value
    # will not be overwritten. Future calls must provide a fallback.
    store.save exchange_rate.calculate(from, to)
  rescue => ex
    # Log error somewhere to help in debugging
    logger.error('counter-cache') { "Location refresh failed: #{ex}"}
    logger.error('counter-cache') { ex }
  end
end

cache.get :usd, :eur do
  # fallback value. Used of original block could not load correct value
  0.8
end

cache.get :get, :bar # => SimpleCache::FallbackError when noting stored

# Explode Operation Mode
#
# Populating the cache may be a process ending condition if it fails.
# Simply execute code as normal. Uncaught errors will propagate to the
# top of the stack.

cache = SimpleCache.new expires: 4.hours do |store, foo, bar|
  # Don't referesh cache if my_thing fails. An existing previous value
  # will not be overwritten. Future calls must provide a fallback.
  store.save my_thing.get(foo, bar)
end

cache.get :foo, :bar # => returns cached value is stored & not expires
cache.get :foo, :bar # => returns value of my thing_get.get(foo, bar) when value not store or expired
cache.get :foo, :bar # => raises an error if my_thing.get raises one