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Welcome to another Swift Deep Dive.
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The goal of this lesson is to really understand the Swift syntax behind functions with inputs.
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Our current problem is that when our xylophone key is pressed, we want to pass over the title of the
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button to our play sound function. To solve this problem,
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we have to learn about function parameters, arguments, and data types.
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Now, if you think back to the greeting function that we created earlier on, all it does is say "Hello!"
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But what if we wanted it to do something slightly different every time?
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What if, say, we wanted it to greet whoever came to our house, so it would have to say "Hello, Angela!" or
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"Hello, Jack!" depending on who's actually at the door,
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how can we pass the name of that person to the greeting function as an input?
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Well, this is how we might create a Swift function that can take an input, so that way, the input can be
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incorporated into the body of the function to do something different every time.
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In programming lingo, the input is called a parameter and the parameter is a bit like a variable without
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a value.
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All we have to do to create it is to give it a name and then give it a data type.
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So here would be the name of a parameter and then it would be a colon, and then the DataType of that
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parameter.
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Previously, when we were creating variables or constants, we've kind of just ignored their data type.
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But in fact, every variable in Swift gets assigned a data type when it's created.
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This means that the variable can only hold data of a particular type.
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So in this case, we have a variable code Angela that's holding a Int type data.
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So you could also create this like so. And here, after a colon, we specify the DataType of the data that's
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going into this variable.
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Now, how come we were able to create our variable like this without assigning the data type?
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Well, Swift also has a capability called Type Inference which means that it's able to infer the DataType
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based on the data that you've put into the variable.
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So in this case, our data is a whole bunch of whole numbers,
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right?
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There's no decimal places and there's no text.
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So this has assigned the type or the DataType of an Int.
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Now, the thing about the data types are that they have to stay the same.
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So if you create a variable that's meant to hold integers,
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well, it can only ever hold integers in its entire lifetime.
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And if you try to fit a different type into the variable that holds integers,
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well, it's not going to fit.
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It's just like those children's toys which you have to fit a particular shape through a particular hole.
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And if you try to fit a star through a square, then it's not going to work.
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Let's see Swift data types and type inference in action.
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Let's go ahead and create a new variable and I'm going to call it myAge and I'm going to set it to
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equal twelve.
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Now, in this case, because we made this variable myAge, store a piece of data that is a whole number, then
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myAge actually gets assigned the data type of int. And we can confirm this by holding down the option
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key and clicking on the name of our variable.
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And you can see that this is the DataType, that it managed to infer from our value right here. Remember
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that we can change the data that's stored inside a variable by simply setting it to equal a new piece
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of data, but we can never change its data type.
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So if I decided this was going to be equal to three, then this is not going to work. It's going to give
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me an error and it's going to say that "Cannot assign value of type 'String' to type 'Int.'
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So myAge is of type int "Three."
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This text here is of type 'String.'
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So there's a mismatch on this line right here.
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Now, if you change the data type of the variable when it was first created, then it wouldn't give you
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any errors.
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It would be able to accept a data type of string.
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But now if we hold down ALT and we click on this, it's now assigned a data type of String and it can
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forever only hold string data.
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So this will now give us an error.
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Now, instead of letting Swift infer which data type we want, we can also assign it at the point where we
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create the variable. And to do that, we add a colon, and then we specify the data type.
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So in this case, it would be a String and all the data types start with a capital letter.
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So we could say it's a String or we could say it has to hold an Int.
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Now, notice how the assigned data type will override whatever value you put in there.
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So this line has a complete mismatch and we get an error. Because this myAge is, of course , of type Int,
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because that's what we said it would be.
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And then we tried to make it hold a string or text data, so that doesn't work, it has to be matching with
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the data type
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we specified. So now that we've understood about these data types,
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let's go back to creating a function with an input.
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When we create our function, we specify the data type of the input that we're expecting. And when we call
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the function, we call the same function name.
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And then in between the round brackets, we specify the input, or in programming,
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it's called the argument.
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So the parameter is the name of the input.
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The argument is the value of the input that we actually pass over when we call or trigger the function.
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Let's create another function called greeting2
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and this function is going to have an input parameter in between these round brackets.
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The input is going to be called whoToGreet and it's not going to have a value, but it does need a data
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type.
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So the whoToGreet which is the name of the person that this function has to incorporate is going to
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be a String data type. And that's it.
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So this is almost like what we did for creating a variable other than giving it a value,
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and we're not using that var keyword.
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Now, we're planning ahead. When this greeting2 gets triggered,
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what do we want to happen?
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Well, we want to somehow incorporate this
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whoToGreet variable.
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So let's say that we had a printed message which just says "Hello,"
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and then it says the "Hello" to the whoToGreet.
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But, of course, in order to insert a variable into our string, we have to use our string interpolation,
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and then we can write whoToGreet inside.
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So now if we call this function greeting2, you can see that it automatically inserts the name of our
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parameter whoToGreet
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and then here we've got a little place holder to specify the value. And whatever we put in here is going
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to be assigned to this variable and then it's going to be printed out right here.
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So let's put in a value of "Angela."
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Now, if I run all of my code and this line triggers, then it's going to print "Hello,"
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and then it's going to add that name Angela.
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So that Angela got added in as the input when we called greeting2,
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so it moves to be the value of this parameter
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whoToGreet,
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and then it gets used inside the body of the function. Now try calling this greeting2 function that
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you've created with some different values and see what you get. So I could say greeting2
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and I could say "Jack Bauer."
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And now if we run our code, you'll see that
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it'll write
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"Hello Angela,"
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"Hello Jack Bauer." Our greeting function is no longer always doing the same thing anymore.
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Instead, it's adapting to whatever input we give it and it's able to achieve different in outcomes.
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So even though, once we've created a function, we can't really change what's going to happen with that
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function ever again,
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but we can still make it do different things
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as long as we provide different inputs. Function with the input vastly improved the reuse ability of
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our functions by providing parts that can be modified.
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So if you think back to the analogy of our housekeeping robot, it'd be really useless if it could only
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ever fetch milk. If we had an item to fetch input, then we can tell it to get bread one day, and then newspapers
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the next day, and we can use that input within the body of the function.
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So now that you've seen how you can create functions with inputs and how you can call them later on,
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it's time to complete the Functions 2 coding exercise and complete that assignment.
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assignment.