use_symbol_to_proc.md

Use Symbol to_proc

The & calls to_procon the object, and passes it as a block to the method. The following calls are equivalent:

%w(john mary michael).map { |x| x.upcase }
#=> ["JOHN", "MARY", "MICHAEL"]

%w(john mary michael).map(&:upcase)
#=> ["JOHN", "MARY", "MICHAEL"]