Method Definition

You've learned that methods are the "verbs" of Ruby. More specifically, a method is a group of expressions that returns a value. A method organizes code into a subroutine, a set of instructions that performs a specific operation.

Method definition assigns a subroutine to a name that can be invoked later. So how do you define a method in Ruby? Let's define a method called add_two_numbers that, well, adds two numbers:

One defines a method by preceding the method's name with the keyword def. Method names conform to the same conventions and rules as variable names:

• They should be in snake case.
• They cannot have special characters.
• They cannot be a keyword.

num_one and num_two are the method's parameters. Parameters are variables declared upon method definition that represent the arguments passed in upon invocation. A method that's invoked with zero arguments would have zero parameters. Method definition ends in end. The code between the def statement and end is the method body. The method body is the subroutine that the method definition encapsulates.

Defining a method does not invoke it, i.e., it does not instruct the Ruby interpreter to execute the code inside the method's body. One invokes custom methods by appending the arguments to the method's name:

Note that the return value is 3. The Ruby interpreter assigns 1 to num_one and 2 to num_two. The order of arguments is important. Arguments are assigned to parameters in matching order. The interpreter adds the arguments as the method's body instructs and returns the result.