Objects have classes
As mentioned before when you run a Ruby program a little universe (space, scope) is being created, and populated with concrete objects (things) as defined by your program. These things interact, and do useful stuff, using certain methods that you call.
Also, each concrete thing (object) is an instance of a general idea or type, and these ideas are called classes.
You can see that objects have classes when you open IRB in your terminal and ask an object for its class:
$ irb > "this is a string".class => String
Objects are concrete instances (manifestations) of classes.
That means that the following sentence is true: In Ruby,
"a string" is a
Hmmmm, yeah, we kinda knew that already, right. However, you can also ask the same question in Ruby:
$ irb > "this is a string".is_a?(String) => true
So, the actual string knows that it is a
String, which in Ruby means that
it is an instance of the class
String. You can do this for any object. E.g.
1.is_a?(Numeric), also returns
true. This is pretty cool.
We also say that an object is an instance of its class. Let’s see what that means.