How to Check Nil Object in Ruby

Ruby allows the programmer to access data using named variables that point to a location in memory. Normally, this works fine, but sometimes an error or other event can cause the variable to point to "nil," a special data type that lets the programmer know that the variable does not point to any data. Programmers can check for nil and react to it appropriately using a special method that all variables inherit.

Instructions

1. Open a terminal. In Windows, click "Start," "Run" and type "cmd." In Mac OS X, click the Spotlight icon and type "Terminal."

2. Type "irb" into the terminal to open the interactive Ruby interpreter.

3. Type the following into the terminal to define a variable as nil in Ruby:

   d = nil

4. Type the following to check if a variable is nil:

   d.nil?

   The result will be either "true" or "false."

Tips & Warnings

• "nil?" will check if a variable is nil, but will still generate an error if it is run on a variable that was never defined at all. In order to check if a variable is defined, you must use the "defined?" operator. Type the following to do so: "defined? d".

References

• Tutorials Point: Ruby Operators
• Ruby Doc: Nil Method