Question

I created the following extension

class String
  def is_a_number? s  # check if string is either an INT or a FLOAT (12, 12.2, 12.23 would return true)
    s.to_s.match(/\A[+-]?\d+?(\.\d+)?\Z/) == nil ? false : true
  end
end

How can I make it work as a chained method?

is_a_number?("10") # returns true
"10".is_a_number? # returns an error (missing arguments)

Update

Thanks sawa, mikej and Ramon for their answers. As suggested, I changed the class to Object and got rid of the argument (s):

class Object
  def is_a_number?  # check if string is either an INT or a FLOAT (12, 12.2, 12.23 would return true)
    to_s.match(/\A[+-]?\d+?(\.\d+)?\Z/) != nil
  end
end

It now works perfectly fine:

23.23.is_a_number? # > true

Thanks guys…

Answer 1

When you write "10".is_a_number?, you already have the object "10" you want to check for, which is the receiver of is_a_number?, so your method doesn’t need to take any parameters.

Because match is an instance method on String, you don’t need to specify a receiver for it. It will just operate on the same object on which is_a_number? was called. Because you know you already have a String object, the to_s isn’t needed either.

Just write it as:

class String
  # check if string is either an INT or a FLOAT (12, 12.2, 12.23 would return true)
  def is_a_number? 
    match(/\A[+-]?\d+?(\.\d+)?\Z/) != nil
  end
end

Ramon’s suggestion that you may want to put your extension on Object rather than on String is a good point if you don’t know if the object you’re testing is going to be a string.

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Also, what you’re describing isn’t really what is meant by method chaining; it’s just calling a method on an object. Method chaining is where the return types of methods are set up so that several methods can be called in sequence e.g in Rails, something like

User.where(:name => 'Mike').limit(3) # find the first 3 Mikes

is an example of method chaining.