thoughtbot/paperclip — pull request #1301 by leomayleomay (2013-07-30 15:46:01+00:00)
Title: Feature: now the "url" option can be a closure or anything respond to "call"

some of the options, like "default_url", "styles", could take a closure as the value, and evaluate the closure at runtime will make the paperclip options really flexible, while "url" is an exception, the pull request is trying to make "url" configurable like the other options like "default_url" and "styles"