How does defining [square bracket] method in Ruby work?

Question

I am going through Programming Ruby - a pragmatic programmers guide and have stumbled on this piece of code:

class SongList
  def [](key)
    if key.kind_of?         


        

Answer 1

It's an operator overloader, it overrides or supplements the behavior of a method inside a class you have defined, or a class the behavior of which you are modifying. You can do it to other operators different from []. In this case you are modifying the behavior of [] when it is called on any instances of class SongList.

If you have songlist = SongList.new and then you do songlist["foobar"] then your custom def will come into operation and will assume that "foobar" is to be passed as the parameter (key) and it will do to "foobar" whatever the method says should be done to key.

Try

class Overruler
    def [] (input)
          if input.instance_of?(String)
            puts "string"
          else
            puts "not string"
          end
     end
end
foo = Overruler.new
foo["bar"].inspect
foo[1].inspect