Block Procs Lambdas map&:(to_s) &:

How &: works? if it is a method, and where is it defined? > It is rails addition to ruby obviously. http://caboo.se/doc/classes/Symbol.html#M003931 Symbol#to_proc This is tricky thing to document. It exploits a ruby syntax quirk where prepending a & to a method argument calls "to_proc" on that object in an attempt to make it eligible to be a block. v.map(&:to_s) Is the same as: v.map { |i| i.to_s } https://www.ruby-forum.com/topic/154453 http://www.reactive.io/tips/2008/12/21/understanding-ruby-blocks-procs-and-lambdas/