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(upbeat music)

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When we started looking at classes,

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I mentioned that there's less need to overload

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functions in Kotlin.

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And that's because Kotlin allows default values

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to be specified for function arguments.

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Now, I didn't say very much about overloading at the time,

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so let's look at what that is in a bit more detail.

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Now, when you overload a function,

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that just means creating another copy of it

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with different parameters.

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So that could be very useful here

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because we could use a different version of drop loot

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and give it the name of the loot.

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So, we could come down here,

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at the moment we've got on line 51,

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the definition for blue potion,

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but in terms of drop loot, we could do something like,

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tim.droploot

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and actually enter the name.

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So, invisibility potion.

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Now, we've got an error at the moment

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because we're passing a string to the drop loot function

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and it expects a loot object.

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Now, if we could pass a string to drop loot,

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then we could drop the invisibility potion,

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even though we don't have a reference to it.

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So what we need to do here,

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is create a version of drop loot

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that accepts the string argument,

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then get it to remove the corresponding item from the list.

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So let's go to our player class,

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we're gonna add this after the existing drop loot method.

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Alright, so we go to start, and drop loot,

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parentheses

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name,

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colon string,

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colon, boolean.

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Then we create the function with

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the left and right curly braces.

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And we'll just do println,

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$name

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will be dropped.

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For now, we're just gonna do return

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true.

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So when overloading a function,

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we create another function with the same name

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but we give it different parameters.

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Now, the compiler checks the parameters,

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and calls the version of the overloaded function

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that has matching parameters.

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So, we've got two versions of drop loot now,

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as you can see.

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So this first one, on line 32,

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takes an argument of top loot

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because we've defined the parameter to be loot.

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Now, the second drop loot, on line 41,

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takes a string argument.

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Now, it doesn't do anything useful yet,

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we're focusing on the overloading mechanism at the moment.

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We'll actually add more code to the second version

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in a minute.

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So go back to main now.

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Notice that the error disappeared.

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And the first time we call our drop loot,

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this code here on line 45,

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actually this is probably a better one here,

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so let's do this one on line 52.

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So, we're calling drop loot there and we're

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and we're giving it a loot instance, blue potion,

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and by doing that, the first drop loot function's called.

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But down here, when we call it with a string argument,

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invisibility potion, in line 58,

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then that's the second drop loot function

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that's gonna be called instead,

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because we're past the argument of top string.

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So let's actually try running this and see what happens.

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And you can see that the other codes executed,

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then right down the bottom,

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invisibility potion will be dropped.

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So that's working in our second version of drop loots,

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obviously being called at that point.

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So that's function overloading,

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you create another version of the function

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with different parameters

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and Kotlin calls the one that matches the argument types.

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Now, there's less need to overload functions in Kotlin

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than there is in Java,

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because again we can use default values

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for the parameters instead.

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But it's still necessary to overload functions sometimes

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and this is one example.

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Alright so we're gonna finish this video up

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by making our overloaded drop loot function work.

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Now, the Kotlin collection classes have a removed

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IF function,

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that we can use to remove an item from the list

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if a certain condition's true.

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So let's actually try that.

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We'll go back to player,

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then player class,

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and our second drop loot function,

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we're gonna do return, we're gonna delete true

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and instead we're gonna return

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inventory.removeIf

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and we're gonna delete the parentheses

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and we're gonna add a code block instead.

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And within there we're gonna put

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it.name == name

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Two equals signs there.

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So that checks each item in the list

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and removes it if the name is the same

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as the name we passed into drop loot.

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Now, it here, where the it.

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well, that refers to the item

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that's currently being checked.

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So if the name of the current item

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matches invisibility potion in our example,

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then the item gets removed from the list.

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Remove if then moves on to the next item on the list

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and repeats the check.

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Now, if any items are removed, it returns true,

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otherwise it returns false.

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Which is what we want the function to do,

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so we can return whatever remove if returns.

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So let's see it working.

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What I'm gonna do is print out Tim's inventory

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at the end of main,

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so we can check that the invisibility potion

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has been removed.

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So we'll go back to our main,

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making sure that I've actually spelled it the same here,

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it's being added as invisibility potion

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and what is being removed is invisibility potion.

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And I'll type tim.showInventory

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and let's see how that goes if we run it.

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And you can see Tim's inventory down there and here

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and invisibility potion,

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which was there on the previous call,

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has now been removed.

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And we've only got the chest armour

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and the ring of protection left.

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So that's working fine.

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Now, just in case you're wondering,

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we don't have to use the return values

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when calling a function.

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So, we could have done the same thing as we did before,

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for the blue potion.

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So we could have done something like this:

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if

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and surround that in parentheses,

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add a code block and then put tim.showInventory,

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and else, your println,

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"you don't have an invisibility potion."

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So if you do that instead,

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and I'll delete that call to show inventory method.

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So let's run that.

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And you can see we get the same result in this case,

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with only the two items left.

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Alright, so I think we got to the end of this video.

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Now, that's probably quite a bit to digest,

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so go back and watch the last few videos a few more times

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if you need to,

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and go through step by step.

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Now, it'll make more sense

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the more times that you go through it.

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And if you watch this and you aren't following along,

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I do suggest that you go back and actually type this in

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as I'm typing it in.

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What I found when I was learning to programme

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was that typing the code in,

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rather than just reading it,

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really helped to consolidate things.

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Back then of course,

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there wasn't really much in the way of video tutorials.

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What we did have was a whole load of computers released

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at around the same time.

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Such as Sinclair ZX 81, Commodore PET,

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BBC computer made by Acorn,

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and a whole lot of other machines.

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And there was also monthly magazines

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and we learned a lot from reading the manuals

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but also from typing in the code

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that was published in those magazines.

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Now obviously you'll make errors when typing the code in

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and debugging the programmes to find the errors

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and make them work, was also a great way to learn.

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So, typing it in seems to solidify the information

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and make it a lot easier to understand.

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So I certainly recommend that you don't just

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watch these videos,

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but you also act and be typing this in

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as the video progresses.

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And it addition, also try modifying the code

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to try different things.

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Start off simple things, such as,

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perhaps adding an extra field to one of the classes,

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then by making other improvements.

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You'll almost certainly get errors

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but sorting out the errors is a great way

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to increase your understanding of how it all works.

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You can't do any damage.

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The worse that will happen is you get an error message.

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Now that wasn't always the case, by the way.

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It was possible to speed up the screen

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on an early computer called the Commodore PET,

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by writing certain values to specific memory locations,

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and if you got that wrong,

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the display would be permanently damaged.

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But that's no longer the case

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and you literally can't do that these days

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with modern computers.

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Basically you can't do any damage to your computer

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with Kotlin, so have fun and try things out.

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Alright, so I've hoped you enjoyed this

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and I will see you in the next video.