numbers.map &:to_s could give different values in the same code—even though its argument doesn’t change It's a family of functions: http://en.wikipedia.org/wik

numbers.map &:to_s could give different values in the same code—even though its argument doesn’t change It's a family of functions: http://en.wikipedia.org/wiki/Indexed_family http://en.wikipedia.org/wiki/Indexed_family