Tuple in Swift

This article explains what a Tuple is and when and where it is used. Happy reading!!!

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Tuple is a group of different values represented as one . According to apple, a tuple type is a comma-separated list of zero or more types, enclosed in parentheses. It’s a miniature version of a struct.

Let’s consider an example: A name say John smith can be declared as a tuple like ("John", "Smith") . It holds the first and last name of a person. You can access the inner values using the dot(.) notation followed by the index of the value:

var person = ("John", "Smith")

var firstName = person.0 // John
var lastName = person.1 // Smith

The type of a tuple is determined by the values it has. So ("tuple", 1, true) will be of type (String, Int, Bool).

() is the empty tuple – it has no elements. It also represents the Void type.

Tuples don’t conform to the hashable protocol. Hence it cannot be used as dictionary keys.

Creating a tuple:

You can declare a tuple like any other variable or constant. To initialize it you will need a another tuple or a tuple literal. A tuple literal is a list of values separated by commas between a pair of parentheses. You can use the dot notation to change the values from a tuple if it’s declared as a variable.

var point = (0, 0)

point.0 = 10
point.1 = 15

point // (10, 15)

Note: Tuple are value types. When you initialize a variable tuple with another one it will actually create a copy.

var origin = (x: 0, y: 0)

var point = origin
point.x = 3
point.y = 5

print(origin) // (0, 0)
print(point) // (3, 5)

Named elements:

You can name the elements from a tuple and use those names to refer to them. An element name is an identifier followed by a colon(:).

var person = (firstName: "John", lastName: "Smith")
var firstName = person.firstName // John
var lastName = person.lastName // Smith

Multiple assignment:

You can use tuples to initialize more than one variable on a single line:

var (a, b, c) = (1, 2, 3)

Returning multiple values:

You can return multiple values from a function if you set the result type to a tuple.

Please note that tuples are passed by value, not reference.

In the above code, for code readability, I’ve used a typealias to pre-define the tuple’s structure.

Tuples for iterating a dictionary getting both key and value:

for (key,value) in myDictionary {
  println("My key is \(key) and it has a value of \(value)")
}

In the above iteration through dictionary example, if we need only the key , then you can use “_” to ignore the value for key.

Note: the _ means “I don’t care about that value”

for (key,_) in myDictionary {
println("My key is \(key)")
}

Decomposing Tuples:

let http404Error = (404, "Not Found")
// http404Error is of type (Int, String), and equals (404, "Not Found")

You can decompose a tuple’s contents into separate constants or variables, which you then access as usual:

let (statusCode, statusMessage) = http404Error
print("The status code is \(statusCode)")
// Prints "The status code is 404"
print("The status message is \(statusMessage)")
// Prints "The status message is Not Found"

If you only need some of the tuple’s values, ignore parts of the tuple with an underscore (_) when you decompose the tuple:

let (justTheStatusCode, _) = http404Error
print("The status code is \(justTheStatusCode)")
// Prints "The status code is 404"

Alternatively, access the individual element values in a tuple using index numbers starting at zero:

print("The status code is \(http404Error.0)")
// Prints "The status code is 404"
print("The status message is \(http404Error.1)")
// Prints "The status message is Not Found"

You can name the individual elements in a tuple when the tuple is defined:

let http200Status = (statusCode: 200, description: "OK")

A tuple inside another tuple:

we’re gonna mix it up by creating tuple which contains another tuple.

let bar: (Int, (Bool, String)) = (1, (false, "Hello"))
print(bar.0) // print: “1”
print(bar.1.0) // print: “false”
print(bar.1.1) // print: “Hello”

An easy way of swapping two values:

var a = 5 
var b = 4 
(b, a) = (a, b)

Where to use tuples

The best place to use a tuple would be when you want a function that can return multiple types. If you’re an Objective-C developer, this concept sounds impossible unless you use an array or dictionary. Previously we’ve had to overcome such problem by either return an NSArray or NSDictionary.

Sources: Medium article, Weheartswift.

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