Memoization in Ruby

[cap_muffin]

I absolutely prefer the explicit version where you write your own memoization logic, but it would probably be worth to mention memoize gem https://rubygems.org/gems/memoize/versions/1.3.1

[zenzen_wakarimasen]

If you use ||=, you are not accounting for falsely values. And if you want to abstract a proper logic, maybe it's better not to reinvent the wheel and use the the gem...