I took it as implied that I was recreating zip. Not re-using it.

I wondered the same thing, until I saw everyone else doing it. I am only just learning ruby.

Read up on the unary & operator. It's operating on the :capitalize symbol. Basically it's making the captialize method into a block.

It's leaning on functionality of Symbol#to_proc to do it. There's a few different pieces that make it up, and http://www.jacopretorius.net/2012/01/symbolto_proc-in-ruby.html seems to be a good in depth writeup of it.

In short though:

• &foo in arguments passes foo as a block to the method as if you'd done { foo.call }. If foo isn't a proc, it calls to_proc on it first.
• Symbol#to_proc is implemented and creates a proc that sends the symbol to the block argument. That is :capitalize.to_proc returns a proc (block) equivilent to { |arg| arg.capitalize }
• Putting it together means [].map { |element| element.capitalize } can be written as [].map(&:capitalize) and it returns the same result.