How to Verify if a Constant is Defined in Ruby

Constants are global values that cannot -- or should not -- be changed once assigned a value. In other words, the value should remain the same throughout the entire program. Like variables, constants follow the same naming rules, but unlike variables, use a capital letter, or letters, instead. To verify if a constant has been defined in Ruby, you can use two different codes. One code confirms via "true" or "false" whether a constant has been defined, while the other confirms whether the constant contains a valid or null value.

Instructions

1. Insert "puts Module.const_defined?(:ConstantName)" into the program code or IRB (Interactive Ruby) to test if the constant is defined. Replace "ConstantName" with the name of the constant. If Ruby returns "true," the constant is defined. If Ruby returns "false," the constant is not defined.

2. Insert "defined? ConstantName" into the program code or IRB as an alternative to the above code. If the constant is defined, Ruby will return "constant." Otherwise, it will return "nil."

3. Use "defined?(Constant).nil?" to create "if-else" statements related to the initialization of the constant. For example:

   if defined?(Constant).nil?
   result if condition true
   else
   result if condition false
   end

References

• "Ruby: Visual Quickstart Guide"; Larry Ullman; 2008
• Ruby-Doc.org: Class: Module