The Elements of a Method

Let's dissect one of the examples from the previous chapter:

9.lcm(3)

9 is the receiver of the method lcm; it is the object upon which the method is called. By using a receiver in conjunction with the . syntax, we invoke or call the method. Method invocation is a call to the Ruby interpreter to execute the method.

3 is the method's argument or input. The argument 3 is passed to the method lcm. Parentheses enclose arguments; commas separate multiple arguments. A method always expects a certain number of arguments. If a method is invoked with the wrong number of arguments, the Ruby interpreter will throw an error. 3.odd?(1) yields this error message: wrong number of arguments (given 1, expected 0).

When we run 9.lcm(3), the shell prints => 9. The value following => is the method's return value or output. 9.lcm(3) evaluates to 9. Altogether, we invoke the lcm method on the receiver 9 with the argument 3, returning 9.