I saw it in some sample Ruby code someone had posted. It was something like:
a.sort_by(&:name)
where a is an array or ActiveRecord objects and :name is one of the attributes.
I have never seen &:name and Ruby's Symbol class documentation says nothing about it. Probably something really simple. :)
Unary Ampersand is address of a function/block/lambda
In this case, it means that the .sort_by function will use each a's element's function named name for comparison
Mostly it used for something else, like this:
[1,2,3].map{ |x| x.to_s } # ['1','2','3']
That could be shortened as:
[1,2,3].map(&:to_s)
So, in your case, a.sort_by(&:name) is a shorthand to:
a.sort_by{ |x| x.name }
