Ruby, pointer to method

Question

Ruby toddler here (3 days playing with Ruby, probably my terminology is yet imprecise).

For study reason I would like to modify the following code to accept ticket.request("triple",10) (or equivalent syntax) in the second last line.

Is it possible (without heavily changing ticket.request)?

ticket = Object.new

def ticket.price
  return 3.5
end

def ticket.triple(c)
  return 3*c
end

# direct call
puts ticket.triple(10)   # ===> 30

# pointer to method
pt = ticket.method(:triple)  
puts pt.call(10)         # ===> 30


def ticket.request(request)    # <=== should it be modified?
  if self.respond_to?(request)
    self.__send__(request)
  end # nil otherwise
end

puts [
   ticket.price,            # direct ===> 3.5
   ticket.request("price"), # safe   ===> 3.5
   ticket.request("name")   # it does not exist ===> nil
 # ticket.request("triple", 10)   <========================= syntax ????
]

score 1 · Answer 1 · answered Aug 02 '19 at 11:31

1

I would do something like this:

def ticket.request(request, *args)
  if self.respond_to?(request)
    self.__send__(request, *args)
  end
end

answered Aug 02 '19 at 11:31

spickermann

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I completely missed it and was quite obvious (later) Thank you – Alex Poca Aug 02 '19 at 11:36
You might want to have a look at this [question about `send` vs `__send__`](https://stackoverflow.com/questions/4658269/ruby-send-vs-send). I thought the OP used `__send__` for a reason. I would suggest using `public_send` or at least `send` if possible. – spickermann Aug 02 '19 at 14:48

Marek Lipka · Accepted Answer · 2019-08-02T11:59:11.647

So, basically you need ticket.request method to take also arguments you want to be passed to subsequent method call? It is possible, if so:

def ticket.request(request, *args)
  if respond_to?(request)
    send(request, *args)
  end
end
puts [
  ticket.price,            # direct ===> 3.5
  ticket.request("price"), # safe   ===> 3.5
  ticket.request("name")   # it does not exist ===> nil
  ticket.request("triple", 10) 
]

*args in method definition works as "take the rest of arguments and store them in args array. In the method call it works in quite opposite way - as "take args array and make it an argument list passed into the method".

Note that I deleted redundant self keywords, as self is default receiver of the message. I also used send method, as it's used more commonly.

Ruby, pointer to method

2 Answers2