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How to Allow Any Number of Arguments in Ruby Methods

August 29, 2012

When calling a ruby method (note: in this article, I’m writing with respect to Ruby version 1.9.x), you must supply the correct number of arguments, otherwise you will get an error. Consider the following:

def method1(x,y)
  puts "Hello, I require 2 arguments."
end

Calling method1(1) will give you an error like the following:

ArgumentError: wrong number of arguments (1 for 2)

If you want to allow zero or more arguments, try using the splat operator

The splat operator (also known as an asterisk ”*”) can be used as follows:

def method2(*args)
  puts "Hello, zero or more arguments in #{args} is all I need"
end

Using *args means that when you call method2, you can supply zero or more arguments.

You can also have a combination of required and optional arguments:

def drive_car(driver_name, *cars)
  cars.each { |c| puts "#{driver_name} drives #{c}"}
end

So calling drive_car("Bob", "mustang", "fiesta", "ranger") outputs:

Bob drives mustang
Bob drives fiesta
Bob drives ranger
=> ["mustang", "fiesta", "ranger"]

You can also use the splat operator when calling a method

So after running the following code,

mycars = ["mustang", "fiesta", "ranger"]
drive_car("Sally", *mycars)

ruby will give the output:

Sally drives mustang
Sally drives fiesta
Sally drives ranger
=> ["mustang", "fiesta", "ranger"]

In an upcoming article, I’ll talk about the order of method arguments with the splat operator.