Show HN: I built a Ruby gem that handles memoization with a ttl

Since using `def` to create a method returns a symbol with the method name, you can do something like this too:

  memoize def expensive_calculation(arg)
    @calculation_count += 1
    arg * 2
  end, ttl: 10, max_size: 2

  memoize def nil_returning_method
    @calculation_count += 1
    nil
  end

Looks good. Id suggest making your `get` wait to acquire the lock until needed. eg instead of

  @lock.synchronize do
    entry = @store[key]
    return nil unless entry

    ...

  entry = @store[key]
  return nil unless entry

  @lock.synchronize do
    entry = @store[key]

Nice! In rails I end up using Rails.cache most of the time because it's always "right there" but I like how you break out the cache to be a per-method to minimize contention. Depending on your workload it might make sense to use a ReadWrite lock instead of a Monitor.

Only suggestion is to not wrap the error of the caller in your memo wrapper.

> raise MemoTTL::Error, "Failed to execute memoized method '#{method_name}': #{e.message}"

It doesn't look like you need to catch this for any operational or state tracking reason so IMO you should not catch and wrap. When errors are wrapped with a string like this (and caught/ re-raised) you lose the original stacktrace which make debugging challenging. Especially when your error is like, "pg condition failed for select" and you can't see where it failed in the driver.

This is neat, thanks for posting. I am using memo_wise in my current project (TableTennis) in part because it allows memoization of module functions. This is a requirement for my library.

Anyway, I ended up with a hack like this, which works fine but didn't feel great.

   def some_method(arg)
     @_memo_wise[__method__].tap { _1.clear if _1.length > 100 }
     ...
   end
   memo_wise :some_method

Can you pitch me on why I would want to use this, instead of Rails.cache.fetch (which supports TTL) powered by redis (with the "allkeys-lru" config option)?

Congrats on shipping your first gem!!

I found this pretty easy to read through. I'd suggest setting a description on the repo too so it's easy to find.

https://github.com/mishalzaman/memo_ttl/blob/main/lib/memo_t...

Will this correctly retrieve 0 values? AFAIK 0 is falsey in Ruby

``` return nil unless entry ```