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Welcome back.

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In this lecture we're going to take a look at a core principle of object oriented programming called

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inheritance.

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Now inheritance is basically just how a class can inherit properties and behaviors from another class.

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The class that is inheriting properties from another class is known as a subclass, while the class

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that is providing the properties and behaviors to inherit is called the superclass.

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So let's do a quick example of inheritance.

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Using tables and meta tables, I'm going to create a new table called animal.

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And this table is going to act as my superclass.

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Now what are some properties that all animals will have?

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Well, let's say all animals will have a name, right?

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We don't know the current name of the animal, so we'll set it to unknown.

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And maybe another property we want all animals to have is a sound they make.

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So maybe a dog, you know, barks, a cat, meows, things like that.

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So we'll just set the silent because again, this is just representing our blueprint for creating an

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animal.

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And again, this is going to be our superclass.

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Now we're going to have to make sure to set the meta method of underscore underscore index equal to

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the animal table.

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That's because we're going to be using this table as our meta table for another class.

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And for it to be able to access these properties, we need to make sure to set the index meta method

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to the table itself.

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Now what's some functions that all animals will have?

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Well, maybe a function that all animals could have is the ability to speak I guess, or emit their

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sound.

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So we'll call this function speak.

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And inside this function we can just print um self dot name.

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The name of our animal says and then we can do self dot sound.

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So that's what our function will do.

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And now we have a basic outline for our superclass.

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So let's go ahead and create another class.

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And this class is going to be our subclass.

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So let's make a class for a cat.

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So this is going to be our subclass.

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Make sure to set the underscore underscore index meta method to the cat class itself.

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Again, because we're going to be using this as a meta table.

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And then in order for this class to inherit all of these properties from the animal class, we need

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to actually set the meta table for this cat class to the animal class.

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Now, our cat class will be able to inherit the properties like the name, the sound, and have access

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to this function like speak.

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So that means we can go down here and set cat dot name equal to cat.

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We can do cat dot sound equal to something like meow.

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And because it's going to be our subclass, there's obviously going to be some things that cats can

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do that other animals can't do.

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So maybe, for example, only a cat can sneak around.

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And inside this function we can just print self dot name.

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Is sneaking around.

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So this function here belongs to our cat class, while this function here belongs to our superclass,

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the animal class.

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And that means we can go ahead and create a new cat object.

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I'll call it my cat.

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And what we'll do is we'll call the set Metatable function.

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Create a new table.

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And set the meta table for this table to the cat class.

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So this is going to be our new cat object.

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And because we've created this new cat object that means we can call functions like speak on it.

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Now, what happens when this function gets called is that the interpreter is going to check to see whether

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or not this table here has the speak function in it.

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When it checks, it's going to see, hey, this index doesn't exist within the my cat table.

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So let's go ahead and check to see if the my cat table has a meta table, which it does.

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And that's going to be the cat table.

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So it's going to go into the cat table and check to see if it has an underscore underscore index meta

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method which it does.

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And it's going to check that table that's attached to this meta method to see if it has the speak function.

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Unfortunately our cat class doesn't have a speak function.

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So it's going to check if the cat table has a meta table with an index meta method, which it does because

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we set it right here.

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So it's going to go ahead and look inside of the animal class and it'll see hey it has an index for

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this table.

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It's going to check this table and it'll see hey this table has the speak function.

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So let's use this function and it'll pass the original table that we called the speak function on to

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the function right here as self.

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So that means this function should print cat says meow.

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And then we can also call the sneak function on our cat table as well.

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So let's go ahead and run the game and let's see what gets printed in the console.

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There we go.

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We get Cat says meow and Cat is sneaking around.

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So this is a very basic example of how you can use inheritance in Roblox Lua.

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It's actually pretty simple.

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All we need to do is set the meta table for any classes to inherit from another class.

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Again, the class that will be inheriting stuff from another class is called the subclass, while the

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class that is giving those inheritable items is called the superclass.

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So I hope you learned a lot and I'll see you in the next lecture.