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We're going to continue where we left off on types by learning how to create our own custom types.

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Creating our own types can be useful for several reasons, but one reason is that creating custom types

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also allows for us to create a default type that is needed for some kind of system.

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For example, maybe we have a custom crafting or inventory system that requires each crafting system

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to be set up in a particular way.

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We can achieve and enforce a particular setup using a custom type.

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Custom types are also incredibly useful for object oriented programming, where we have a class and

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enforce the return of a constructor to produce a variable of a specific custom type, and we can also

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create custom types for the parameter section of a constructor.

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So someone knows exactly what needs to be fulfilled and what is optional to give to the constructor.

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You'll see us use custom types later in the course, but just know that Roblox gives us the ability

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to do this, even if it seems a little useless at the moment.

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So to create a custom type, we can use the keyword type, and then afterwards we can just pass the

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name like we would for a variable.

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So I'll call this one example table.

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And then we can set it equal to an empty table.

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And then we could also pass some parameters in here that this type may have.

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So we could do example param.

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And this parameter needs to be a number.

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So now we have this custom type here that any variable we set to have this type must be a table.

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And it has to contain this example parameter in there with a number attached to it.

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So if I create a new variable like some table and I set it to be of the type example table, as you

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can see now, it appears when we go out and look for types, and then we can set it equal to a new table.

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And then we can create the example parameter.

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As you can see it shows up right here.

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And it tells us it needs to be a number because we have set it to be of the type example table.

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So we can go ahead and fulfill this just like that.

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Now the table is stored at.

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This variable is considered sealed, meaning that you can't add or you cannot remove any parameters

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from this table.

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As an example, if I index some table and try to add another parameter like, we'll call it another

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param.

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And we set it equal to a number like three.

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As you can see, we're going to get an error here.

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And it says cannot add property.

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Another parameter to example table.

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This is because this table is sealed.

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Tables are sealed when we explicitly define a type for a table to be.

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Tables are unsealed when we just create them like this.

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So if I do another table.

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And just do that.

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This table is considered unsealed and we can add and remove anything we'd like from the table, because

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we didn't explicitly define a type for this table.

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So this is unsealed and the one above is sealed.

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As another example, I'm going to create a type and I'm just going to call it inventory.

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And inside of this table I can define some things that an inventory would have.

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For example it may contain a table that has, you know, items inside of it.

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So what we could do to be able to add multiple things to this items table is that we could define that

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the key has to be a number.

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And then we can define the value attached to this number is a string.

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And then maybe we could add an optional parameter to this table, like the max capacity of the inventory.

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And we'll set it to a number.

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And then we put that question mark there to make this an optional parameter.

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Now when we go to create a new inventory, we could do new inventory.

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Declare it of the type inventory and set it equal to a table with some items in it, and just set it

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to, I guess, an empty table.

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From this point, we can index new inventory and get the items table, and now we can add new index

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value pairs.

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For example, at this first index I could create something like I don't know, we have a rock right?

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And then maybe at the second index we have an item like, I don't know, wood.

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And then at the third index.

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We have something like a crystal.

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And then once we've created these items in this inventory, we can go ahead and print them out in the

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console.

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So new inventory, we can get the item at the first index.

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And then when we go to run our game, we should get rock printed in the console.

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And we do.

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Perfect.

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And of course, one more thing to take a look at is that when we type out new inventory, we can see

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it is of our custom type inventory.

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So this was just a brief overview of how we can create our own custom types in Roblox.

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While it may seem a little useless at first, there are going to be quite useful when we're going to

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start using them in module scripts and our classes.

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See you in the next lecture.