"Ruby Operators and Control Structures" was retired on November 27, 2017. You are now viewing the recommended replacement.
Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Well done!
You have completed Ruby Objects and Classes!
You have completed Ruby Objects and Classes!
Preview
When using variables inside classes, only instance variables, which are prefixed with the `@` character, will be visible to all of the methods in the class. A variable that only exists inside of a code block or method is called a local variable. The whole concept is called scope.
Code Samples
class Name
attr_accessor :title, :first_name, :middle_name, :last_name
attr_reader :first_and_middle_name
def initialize(title, first_name, middle_name, last_name)
@title = title
@first_name = first_name
@middle_name = middle_name
@last_name = last_name
end
def full_name
@first_and_middle_name = @first_name + " " + @middle_name
@first_and_middle_name + " " + @last_name
end
def full_name_with_title
@title + " " + full_name()
end
end
name = Name.new("Mr.", "Jason", "", "Seifer")
puts name.full_name_with_title
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
When we create different variables inside
of a class,
0:00
not every method can see the variables
that we use.
0:03
If we wanna make a variable visible to
different methods inside of a class,
0:08
we call it an instance variable.
0:12
That means that the variable should be
visible to
0:15
the whole instance of the class.
0:18
If we want a variable that's only visible
inside of the method or
0:21
block that we're working with, that's
called a local variable, and
0:25
this whole concept is called the scope of
a variable.
0:29
Let's see how that works now using
Workspaces.
0:34
So, here's our Name class, and
0:38
let's talk a little bit about local versus
instance variables.
0:40
So, here we are in the full_name method,
and we also have full_name_with_title.
0:46
Let's go ahead and
0:51
pretend that we were creating a couple
different variables inside of this method.
0:53
So, let's say that we wanted to assemble
the first and middle name.
0:59
We could create a variable that says first
_and_middle_name.
1:05
We generally wouldn't do something like
this, but just follow along for a second.
1:10
[BLANK_AUDIO]
1:14
We now have access to this first
_and_middle_name variable right here.
1:21
So, what we could do is, I'm gonna comment
this out, and
1:26
we could say first_and_middle_name plus
space plus @last_name.
1:32
And that should still return the correct
item.
1:42
Now let's go ahead, get this out of here
for now.
1:46
So let's run this by typing ruby name.rb.
1:50
And it's printing the same thing, which is
what we wanted.
1:56
But we do not have access to this
first_and_middle_name variable
1:59
outside of this full_name method.
2:05
The only way that we would have access to
it
2:09
would be if we made it an instance
variable.
2:12
And we can see this if we use irb.
2:15
And we can do a shortcut to what I showed
you earlier where you type in load and
2:20
the path, and by typing irb -r name.rb.
2:25
Oops, looks like I forgot the path.
2:31
[BLANK_AUDIO]
2:33
Okay.
2:37
Now let me go ahead and create this name
variable.
2:39
[BLANK_AUDIO]
2:43
Now we can see printing out full_name
works when we call the method.
2:54
But if we were trying to call
first_and_middle_name,
2:59
this would not work.
3:02
[BLANK_AUDIO]
3:03
This doesn't work because it is just a
local variable.
3:06
[BLANK_AUDIO]
3:10
If we wanted to change it to an instance
variable, we would then have access to it.
3:13
Now, since we changed this file,
3:22
we're going to have to reload it into our
irb session.
3:24
Now let me go ahead and create a name
again.
3:30
[BLANK_AUDIO]
3:32
Now when we call first_and_middle_name,
3:44
we're getting this undefined method again
still.
3:47
And the reason is we haven't written an
attribute reader for it.
3:51
So let's go ahead and do that.
3:55
[BLANK_AUDIO]
3:56
And we'll reload this.
4:04
[BLANK_AUDIO]
4:05
And we can see that that's nil.
4:20
If we call full_name, it will have been
set when we called the full_name method.
4:23
And now we can see first_and_middle_name
is correct.
4:32
So, visibility of variables is something
very important to keep in mind,
4:37
and this is referred to as the scope of a
variable.
4:43
The scope, meaning where we are in the
method and what's visible variable-wise.
4:47
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