Original subtitles

0 Now in the last lesson, we covered flat buttons and the void callback that they expect. 1

We also used the print function and gave it an input, or rather an argument. 2

So in this lesson, I wants to quickly cover Dart functions. 3

So if you already know what an argument is, what return does and what a function does, then feel free to 4

skip this lesson and head over to the next one where we continue building out our Flutter app. 5

But for those guys who are staying with me, functions as you can guess from the name, are there to give 6

your app or you give your program some functionality, right? Now, 7

in this lesson, I want to talk about functions in the most fundamental sense and when we using functions 8

as programmers, 9

fundamentally, we're trying to package bits of code together into a block and to call that block of code 10

repeatedly, saving ourselves from typing the same code again and again and again. 11

So for example, if you had a little housekeeping robot, this guy. His name is Bit Bob. And he does a number 12

of things right? 13

For example he'll go and get you milk every day. But you have to tell him how to do it. 14

You have to tell him to leave the house, move right to blocks, move up four blocks, then move right to blocks, 15

get the milk, come back. And you have to specify all these instructions to him because he's a robot and 16

he doesn't understand contextual information like go to the store and get me some milk. Now if you had 17

to do this day after day after day every single time you wanted milk, your fingers would start hurting, 18

and you wouldn't want to keep typing out the same instructions. 19

Right? 20

So what can you do? 21

Well we're programmers. 22

We're born to be lazy. 23

So what we can do instead, is we can take all these instructions that the robot understands, and we can 24

package it into a block of code. 25

Now a block of code, in many many programming languages, is represented by code that inside a set of curly 26

braces. 27

Once we've got all our instructions inside our curly braces, we can give that block of code a name. 28

And in this case we've called it getMilk. 29

Now every time I need some milk, I can tell the robot get milk and it'll know what to do because it 30

will find this function called getMilk, and look inside it to see what it should do. 31

It's almost like I'm creating a recipe, right? 32

It's like, I want to eat cookies, but I don't want to bake cookies. 33

So let me write down a recipe and give it to my housekeeping robot, so that they can make it for me. 34

And that recipe or the name of the recipe is basically the name of our function. In Dart, the way that 35

you would create the function looks like this. 36

We've got the name of the function which is called getMilk, and then we've got the curly braces which 37

enclose all of the things that should happen when this function gets called. 38

And then later on when we actually need to use it, we will call the function or tell the computer to 39

execute all of this by writing something like this, giving the name of the function. 40

Now this is called a named function. 41

Well it makes sense because it's got a name. 42

Right? 43

We can identify it by what it's called. 44

Now if we dropped everything other than just the core parts, namely the parentheses and the curly braces 45

and all the instructions, then this would become an anonymous function, because it doesn't have a name. 46

Right? 47

And these anonymous functions are legion. 48

No just kidding. 49

These are anonymous functions are actually very useful. 50

They allow us to tell the computer to do something without explicitly having to create this entire function 51

and give it a name and call its name. When we were coding up our onPressed which expected a void callback, 52

it essentially wanted an anonymous function. 53

We passed in the two empty parentheses, and we gave it the block of code that we want to be executed 54

when the button got pressed. This is all you need to know about functions so far to be able to understand 55

what's happening in our flat 56

button. A little bit later on when we level up and we talk about functions in more detail, we'll talk 57

more about what goes in these parentheses namely some inputs into the function. And also we'll talk about 58

the return statement when we want our function to output something. 59

But for now, just know that this is anonymous function. 60

It has a set of parentheses and a set of curly braces. In the curly braces 61

we say what should happen. So now that we're all caught up, in the next lesson we're gonna get back to 62

coding up our dice app. And we're going to get our button to change our dice images to actually make the 63

app work. 64

So for all of that and more, I'll see on the next lesson.