How can I 'join' an array adding to the beginning of the resulting string the first character to join?

Question

I am using Ruby on Rails 3 and I am trying join an array with the & character. I read the Ruby documentation about that.

My array is:

Answer 1

A slightly modified form of the answer you provided may be less computationally intensive, given the size of your array.

(['']+Array.wrap(classes)).join('&')

This works for whether classes is a type Array