We've already covered the basics in our introduction to classes in Ruby. Here's a quick summary:

• Classes act as templates for the creation of objects, specifying their state and behaviour
• An object created by a class is called an instance of that class
• A class is itself an object, and an instance of the class Class

When talking about objects, we often shorten "this object is an instance of the class User" to "this is a User." As far as we're concerned, both sentences mean the same thing and the phrase "is a" is equivalent to "instance of".

What's more, Ruby actually gives us a method called just that. Let's look at an example.

Example Code:

puts "A String".is_a?(String) # true puts 1.is_a?(String) # false

[reset] Need a hint? See the Solution

Hint

Output Window

As you've probably guessed, Object#is_a? accepts a single parameter - a class. Object#is_a? has an alias, Object#kind_of?. They're identical in every respect so you're free to pick whichever reads better in a given context.

Here's an exercise that requires you to combine Object#is_a? with something you've already learned about classes. As always, your objective is to make the tests pass.

def know_it_all(object) # Your code here end

[reset] Need a hint? See the Solution

Hint

Remember: Calling the method class on any object will give you its class.

Output Window