Structs

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Goal

You will define a Swift struct, give it stored properties, and create an instance. After this page you will recognize the shape every SwiftUI view is written in — because every SwiftUI view is a struct.

Prerequisites

• Swift values and variables
• Functions and trailing closures

What a struct is

A struct is a type you define yourself by listing the data it holds. Each piece of data is called a stored property. Structs in Swift are value types — when you pass a struct around, the receiver gets its own copy, not a reference to the original.

Two things make structs the right tool for SwiftUI views:

1. They are cheap. Creating one is roughly free.
2. They are immutable by default. SwiftUI re-creates views constantly when state changes; values that can't accidentally mutate are safe to throw away.

Swift gives every struct a memberwise initializer automatically — a constructor that takes one argument per stored property, in declaration order.

Try it in a playground

In SwiftBasics.playground:

import Foundation

struct TodoItem {
    let title: String
    let isDone: Bool
}

let task = TodoItem(title: "Buy milk", isDone: false)

print(task.title)
print(task.isDone)

Run it. Output:

Buy milk
false

TodoItem(title:isDone:) is the memberwise initializer. You didn't write it — Swift generated it from the property list.

You can add methods inside the struct too:

import Foundation

struct TodoItem {
    let title: String
    let isDone: Bool

    func summary() -> String {
        let marker = isDone ? "[x]" : "[ ]"
        return marker + " " + title
    }
}

let task = TodoItem(title: "Walk dog", isDone: true)
print(task.summary())

Output:

[x] Walk dog

This is the shape a SwiftUI view takes: a struct with properties and a method (called body) that returns the rendered UI. We'll see that next.

Next → The View protocol