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Instance Variables and Local Variables4:54 with Jason Seifer
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.
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
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
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