Swift Basics

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Expressions

Using the swift REPL, you can type expressions to have them evaluated.

1 + 2
# $R1: Int = 2

Variables

You can declare variables inline with the var keyword.

var x = 30
# x: Int = 30

Note how x is of type Int because we initialized it with an integer. You can
also declare variables as constants, meaning their values cannot change.

let y = 50
# y: Int = 50

Here y is also an Int, however you cannot set y to a new value since it is declared with let.

If you don't specify an initial value, you must declare the type of variable, like this:

var count: Int
# count: Int: 0

count received the default value for Int variables because we did not specify one.

You can work Doubles similarly:

var price: 0.5
# price: Double = 0.5

var subTotal: Double
# subtotal: Double = 0.0

Strings and Characters

Strings are easy to work with in Swift.

var string = "hello"
var letter: Character = "A"

You can index strings just like arrays, and any NSString methods just work like they did before.

Arrays

You can declare arrays with square brackets:

var items = [1, 3, 4]
# items: Int[] = size=3 {
#   [0] = 1
#   [1] = 3
#   [2] = 4
# }

You can append items to an array:

items.append(6)
# items: Int[] = size=4 {
#   [0] = 1
#   [1] = 3
#   [2] = 4
#   [3] = 6
# }

... and even append other arrays...

items += [7, 8]
# items: Int[] = size=3 {
#   [0] = 1
#   [1] = 3
#   [2] = 4
#   [3] = 6
#   [4] = 7
#   [5] = 8
# }

Using Let with arrays

let items = ["Apple", "Banana"]

items is immutable, and cannot change.

Slicing arrays

var numbers = [ "a", "b", "c", "d", "e", "f", "g" ]
numbers[0..&lt;2]
#  String[] = size=2 {
#    [0] = "a"
#    [1] = "b"  
#  }
#

If you want the range to include the last value, then you use ... like this:

var numbers = [ "a", "b", "c", "d", "e", "f", "g" ]
numbers[0...2]
#  String[] = size=3 {
#    [0] = "a"
#    [1] = "b"  
#    [2] = "c"
#  }
#

Dictionaries

var gradebook = [ "Al": "A", "Joe": "B", "Charlie": "D" ]
gradebook["Charlie"] 
#> String? = "D"

Checking to see if values exist in the dictionary:

if let grade = gradebook["Ben"] {
  // doesn't get called
}

if let grade = gradebook["Al"] {
  println("The grade is \(grade)")
}

Looping

Arrays:

for item in items {
  println("The item is \(item)")
}

Dictionaries:

for (student, grade) in gradebook {
  println("\(student) has a \(grade)")
}