All language subtitles for 5. [Dart] Functions - Part 2

All right.
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So in the last module, we talked about Dart functions.
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We talked about part one of Dart function. And those were the simplest of functions.
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They simply package a whole bunch of code together inside some curly braces, so that when you want all
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of these instructions to be executed in one go, you can simply call the function by specifying its name.
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But it's rather curious how we've been using these parentheses.
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We've always left it empty.
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What are they for?
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Well I like to think of these types of functions as the most basic type of functions.
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And there's actually three different levels of functions if you will. If this is the most basic, then
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let's call it the vanilla flavor of function.
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Now we're coming across the next flavor of functions. And we saw this in the code in the last lesson.
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We saw that we could specify an input to our function inside those parentheses, and we could use that
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input inside the function.
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And this makes our function far more adaptable because we can now get it to do slightly different things
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by providing a different input.
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So now let's talk about part two of Dart functions. We're leveling up our Dart functions. So coming back
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to our little robot,
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what if instead of just telling him to go and get milk, we could actually tell him how many bottles of
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milk to get? And we would do that by calling the function getMilk and providing an input inbetween
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the parentheses.
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So if we wanted two bottles, we would write 2,if we want four bottles we would write 4.
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So that means that our little robot is a little bit more intelligent
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now. We don't have to always get one bottle of milk every single time it goes to the store. Instead of
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having a function that looks like this where it's just a whole bunch of instructions packaged together
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into a block with a name,
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we now have some inputs inside the parentheses. And those inputs can be used inside the block of code
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to change the functionality of that block of code.
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And now we can use that input inside the function.
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For example we could calculate the cost of getting X number of bottles, right?
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If they called getMilk and they wanted two bottles of milk,
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then if one bottle of milk was £1.5, then that would be £3 for the total cost of
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the milk.
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Basically, we now have this input or some might call an argument, and this is something that will modify
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the functionality of this function. But there's two important parts to this.
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One is you have to specify the data type that goes into this function, and you also have to give it a
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name so that you can refer to it when you need it inside the curly braces of this block of code.
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Now when you call the function, it also looks a little bit different.
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We still call it by its name, but inside the parentheses instead of having an empty set up parentheses,
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we give it an input.
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So let's say we want to get two bottles of milk.
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Well then the input now flows in to the function, and it becomes stored inside this name called bottles.
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Now the first thing it checks is to make sure that it definitely is getting the right data type as the
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input. So it's definitely getting an integer
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in this case, and 2 is a whole number,
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so that's completely fine.
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So when we call getMilk passing in the input of 2, it's almost like we're creating a new variable
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that is of data type int.
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It has a name of bottle, and it has a value of 2.
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So now inside the curly braces of this function, we get to use this new variable, including to calculate
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the cost or do whatever we will with that input.
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Now it's your part to apply this in practice. Head over to a dartpad and I want you to create a greeting
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robot.
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Now this greeting robot is pretty simple.
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All it needs to do is to print a greeting such as 'Hello Angela' to the console. Notice here, I'm calling
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a function called greet, and I'm passing in the input, that's my name, but it could also be anybody else's
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name. And this name in here has to be put after a 'hello' or a 'how do you?' do or 'howdy'.
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And it has to be printed into the console.
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So go ahead and create this great function that achieves this functionality. Pause a video and complete
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this challenge.
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All right.
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So we start out creating our function with the keyword void.
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And then we give our function a name.
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So in this case it's going to be called greet,
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because that's how we said we would be using it.
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Now we have a set of parentheses, and inside here,
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we specify the argument or the inputs to this function.
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Now in this case, we want to be able to pass in a name.
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So that later on, we can simply execute the functionality, that's print. And we can say something like hello
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and we might be able to add a name into there. So that we'll go in here. And the data type that our greet
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function will accept is a string, because it's going to be a name,
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right?
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It'll be Angela or Jack Bauer or whatever it may be.
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And then we have to give that a name, and we'll call it personToGreet.
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And now, we get to use this personToGreet inside our function.
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So every time I say inside, it just means inside the curly braces. And we can use our $ to add
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that personToGreet to the end of our hello sentence. And let's cap it off with a semicolon.
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And now when I hit run, it will go into main to see what it needs to do.
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And we tell it to call the greet function, so it finds this great function. We give it the input or an
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argument of Jack Bauer.
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So Jack Bauer then goes inside here, and now personToGreet is equal to Jack Bauer.
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So now inside this function when it looks to see what it needs to do, it'll print out the words hello
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and the personToGreet, which in this case is Jack Bauer.
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So it will simply replace it right here.
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And so now effectively, we've done the same thing as write print, Hello Jack Bauer.
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But it's so much more flexible because we can specify any input and it will simply run it through the
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same process.
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I hope that makes sense. But you might also realize that there's a bit of a weakness here.
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What if we had two things here?
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What if we said we had another greeting,
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right?
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What if, you know, I wanted to be able to
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define what I say to this person?
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Say I want to be able to say, you know, instead of hello, I might want to say good bye,
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right?
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So let's use our greeting variable here, and then we've got our personToGreet here. And here, I can simply
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write Jackie and I'll say howdy. And I'm going to separate them with a comma.
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So now if we click run, you can see that what gets printed is Howdy Jackie.
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So if I say how do you do, then our function ends up printing
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How do you do
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Jackie.
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We can use as many inputs as we want but at some point it gets a bit confusing right?
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We're calling this function, which one should go where? Is it
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this one that should go first
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or is it the other one that has to go first?
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And notice that this actually matters, the order matters because. If I click run, now it'll instead print
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Jackie
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How do you do.
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Right?
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The first part is this greeting, and the second part is this personToGreet. So to minimize confusion,
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one of the things that you can do is to add this name into the greet function as an argument name.
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So then you would call this function like this.
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You would say greet with the greeting,
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that is How do you do.
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And with the personToGreet being this one.
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And when we've been using a lot of functions that came from the Flutter team, this is what we've been
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seeing. Now in order for this to work, all you have to do is just add a set of curly braces around your
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input parameters. And that allows you to use these names that you've defined in the input when you call
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the function as well as when you're inside the function.
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And this means that there's less confusion when you're actually trying to trigger the functionality.
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So whereas previously we simply had the data type and the name of the input argument,
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now we're adding some curly braces around the input arguments where we want to use their name.
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And so now what when I call this getMilk function, it won't let me give it an input unless I specified
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which argument the input was for.
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But it also means I can swap things around now and the order no longer matters.
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I can say that the personToGreet is Jackie and the greeting is going to be how do you do.
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And now if I hit run, it achieves exactly the same thing. But because I now can associate my data with
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the argument,
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it's much much clearer what's actually happening with my function.
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So now that you've learned all about functions in Dart, let's head back to completing our Xylophone app.