First method works just fine if I want to calculate what was his age last year, ...

levosmetalo on April 28, 2014 | parent | context | favorite | on: Uncle Bob on DHH: Monogamous TDD

First method works just fine if I want to calculate what was his age last year, and what will be his age at the year of 2021. The second method doesn't, so these are not even functionally equivalent.