This course will be retired on June 1, 2025.
Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Preview
Start a free Courses trial
to watch this video
The Object and Kernel classes are the root of all Ruby class and object functionality. Object is the base class that all Ruby classes inherit from. The Kernel module is included by the Object class and contains methods that can be used in all classes.
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
The Object and
0:00
Kernel classes are the root of all
Ruby classes and Object functionality.
0:01
Object is the base class that
all Ruby classes inherit from.
0:07
The Kernel module is included
by the Object class, and
0:12
therefore contains methods that
can be used in all classes.
0:16
Let's go ahead and take a closer look at
Object and Kernel now using workspaces.
0:21
Now here's the documentation for
Kernel, and
0:27
then in this other tab,
we have the documentation for Object.
0:30
Let's go ahead and
take a look at Kernel first.
0:34
Now the documentation tells us that
the Kernel module is included by
0:38
the class Object, so its methods
are available in every Ruby object.
0:43
Now, we can find the instance method
documented in the Object class, but
0:49
the module methods are documented
in the Kernel class documentation.
0:53
Since they're module methods,
and Kernel is included,
0:59
we have access to all of these
basically anywhere in Ruby.
1:03
And here we can see just some of
the methods that we have available.
1:09
For example, Array will return
any argument as an array.
1:12
So let's go ahead and try this in an IRB
prompt which I have up over here.
1:17
We'll say, Array.
1:23
And just pass in one argument here.
1:24
1, and it returns an array.
1:28
Same thing if we pass in a string.
1:33
Now, that's not a very interesting method,
but we can see that that works with array,
1:36
complex, float, hash, integer,
rational, and string.
1:41
So we could pass in an object and
it would be returned as a string.
1:47
Now some of these other methods
in here will tell you the name,
1:52
for example,
of the current method as a symbol or nil.
1:58
We also get methods like block_given
which we'll send into any method.
2:09
You can say if there is a block_given
go ahead and work with that.
2:15
Or if not, do something else.
2:19
But let's scroll down a bit to some
of the interesting methods that we've
2:22
seen before.
2:25
For example, here is the puts method.
2:31
Now, we've seen that several times.
2:36
And that allows us to print
something to the screen, like Hello.
2:38
And it also returns nil.
2:43
Now, what's interesting about this is
this is part of the Kernel module.
2:45
And we have seen other ones before.
2:51
Printf, puts, print, and p as well.
2:54
Now, if we take a look at
the Object class, here,
3:00
we have access to some
parts of the Kernel module.
3:05
Now, here's something that's interesting.
3:09
Object is the default
root of all Ruby objects.
3:11
So every object is inherited
from Object or BasicObject.
3:15
Now when we're working with classes, we
can ask the class what its superclass is.
3:21
So for example, we could say String,
which we're used to, and
3:28
ask what class that inherits from
with this method superclass.
3:34
We can see that that inherits from Object,
which means that strings are going to have
3:37
access to all of Object's methods,
and Object includes Kernel as well.
3:43
So there are some interesting methods
that we have inside of Object.
3:49
For example,
the methods method returns a list of
3:54
all the public and
protected methods of an object.
3:59
So for example,
we could have a new string, And
4:08
ask this string what its methods are.
4:13
And this will show you everything that
String supports, and it returns an array.
4:17
So since it's an array,
We can sort it, and
4:24
that will now be in alphabetical order.
4:28
Now, if we go back and
look at the Object methods,
4:32
Here's an interesting
one called respond to.
4:39
And what respond to will do is tell you
if an object responds to something.
4:42
And when we ask if it
responds to something,
4:48
that will mean that any of these
methods work on a given object.
4:51
So, for example we could say,
4:55
does this string respond to strip?
5:00
Now, we saw that in the methods,
so it returns true.
5:06
But if we made something up,
it will return false.
5:10
Now, we can ask any object for
these things,
5:15
because all objects descend
from this Object class.
5:19
Which is also where we find
this nice inspect method.
5:25
Inspect is a default on pretty
much any class, string.inspect.
5:29
And it's nothing.
5:35
Just an empty string right here.
5:36
The backslashes indicate
an escape character.
5:38
If we had had our own class,
it would print out something like this.
5:41
We can ask classes if they
are an instance of a certain class.
5:47
And that will return true.
5:57
And for example if we look at a string and
ask if it's an instance of Array,
6:03
that will be false.
6:06
There are a lot of methods here inside of
the Object class and the Kernel module.
6:11
Go ahead and
look through the documentation and
6:18
try some of them out now
in your own workspace.
6:20
We didn't cover all of the Kernel
methods in this video.
6:24
Try experimenting with some of them
on your own now using workspaces.
6:27
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up