Swift Structures

Swift Structures

Structures are essentially a way to group together information to represent something in our app. A model of data or a function.

Structures are named with capital letters (MenuItem, SpongeBob).

New structure → add a new file. Define your structure in that new file.

Empty structure

struct MenuItem {
}

Structure with variables

struct MenuItem {
    var name:String  // Properties of the Structure
    var price:String
    var image:String
}
 
// This creates a custom data type.
// For example, var array:[MenuItem]
 
struct MenuItem {
    var name:String
    var price:String = "$2.99"
    var image:String
}
 
// If you pre-define the values, then don't need to define during an instance.

Structure with functions (methods)

struct MenuItem {
 
    func printHello() {  //  Methods of the Structure
        print("Hello World!")
    }
 
}

Identifiable protocol

Original page had a screenshot here.

Identifiable is a protocol that a structure needs to conform to in order to be used in a List. It gives the system a way to ID each item so it can differentiate one from another.

// We have to make our structure conform to Identifiable Protocol
// Create a new id property, and set a UUID instance
// UUID is our special data type
// UUID() is an instance that creates a UUID with RFC 4412 version 4 random bytes
 
struct MenuItem: Identifiable {
    var id: UUID = UUID() // Creates a random ID that is assigned to the menu item
}

Instances

Instances are the different things you can create from the blueprint (structure).

// Create a new instance
// Start with the name of the structure that you want to create an instance of
 
MenuItem(name: "Onigiri", price: "$1.99", imageName: "onigiri")
 
// Assign the instance to a variable
 
var firstItem: MenuItem(name: "Onigiri", price: "$1.99", imageName: "onigiri")

Accessing instances (dot notation)

Dot notation accesses information. Dot just means self.

// Taking variable information
print(firstItem.name)
>> "Onigiri"
 
// Taking function information
firstItem.printHello

See next

• SwiftUI-Layout — Lists iterate over arrays of Identifiable structures