Day 2 - Swift Booleans and String Interpolation

In today’s lesson, we will look at Booleans, a data type that stores the result of logical conditions, and Interpolation, an important feature that we can use in String expressions.

How to Store Logical State: Boolean #

The Boolean type is quite simple. It can only store true and false.

Boolean data can be created as follows. It has no values other than true and false.

let goodDogs = true
let gameOver = false

In fact, we saw this data type in the subjects we studied on day 1.

let filename = "paris.jpg"
print(filename.hasSuffix(".jpg"))
//OUTPUT : true

let number = 120
print(number.isMultiple(of: 3))
//OUTPUT : true

hasSuffix() checks if “.jpg” is present at the end of the string “paris.jpg” in the filename variable and returns true if it is present.

Similarly, isMultiple(of:) checks if the value 120 in the number variable is a multiple of 3 and returns true.

Boolean expressions cannot be subjected to arithmetic operations, so arithmetic operators cannot be used. But with Boolean expressions the ! operator is used, which means “NOT”. This operator reverses the value.

var isAuthenticated = false
isAuthenticated = !isAuthenticated
print(isAuthenticated)
//OUTPUT : true
isAuthenticated = !isAuthenticated
print(isAuthenticated)
//OUTPUT : false

There is a function toggle() that can be used for bool expressions. This function inverts the value of the bool expression. The toggle() method does the same thing as the ! operator, it just makes it easier to read in long and complex code.

var gameOver = false
print(gameOver)
//OUTPUT : false
gameOver.toggle()
print(gameOver)
//OUTPUT : true

String Interpolation #

There are 2 methods for concatenating string expressions;

• Use of the + operator
• String Interpolation

Using the + Operator #

The use of the + operator with String is quite simple. You can combine two (or more) string expressions.

let firstPart = "Hello, "
let secondPart = "world!"
let greeting = firstPart + secondPart
print(greeting)
//OUTPUT : Hello, world!

We can continue to do this merging process one after the other.

let people = "Haters"
let action = "hate"
let lyric = people + " gonna " + action
print(lyric)
//OUTPUT : Haters gonna hate

We can even take things a bit further and do something like this.

let luggageCode = "1" + "2" + "3" + "4" + "5"

When you examine the above example, the last string expression we will have will be 12345. But here we encounter a problem. Swift will not do this concatenation all at once. The path it will follow will be as follows:

• “12”+”3”+”4”+”5”
• “123”+”4”+”5”
• “1234”+”5”
• “12345”

So the concatenation will be done step by step. String concatenation with the + operator is only suitable for low-step concatenations. But what if we need more? In that case, String Interpolation will come to the rescue.

String Interpolation #

Interpolation is quite simple to do. We can solve it with a backslash and 2 parentheses. Also Interpolation is not only String, it can combine Int, Double, Bool and many other things with String.

let name = "Taylor"
let age = 26
let message = "Hello, my name is \(name) and I'm \(age) years old."
print(message)
//OUTPUT : Hello, my name is Taylor and I'm 26 years old.

As seen in the code above, we were able to insert an Int value (age) directly into a String expression.

This is where the difference from the + operator comes in. For example, if we were to write a code like the one below, this code would not work. Because only String expressions can be combined with the + operator.

// CAUTION THIS CODE IS BUGGY. XCODE GIVES ERROR.
let number = 11
let missionMessage = "Apollo " + number + " landed on the moon."

But if we want to combine the above example with the + operator, we can do the following.

let missionMessage = "Apollo " + String(number) + " landed on the moon."

But there is a faster way:

let missionMessage = "Apollo \(number) landed on the moon."

You can also read this article in Turkish.
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