Structured Concurrency

Armaan Khan — Mon, 05 Oct 2026 12:32:16 +0000

Lesson - 8 Structured Concurrency(Swift Concurrency)

So far we have created independent tasks.

Task {
    // task
}

what if we wants task to be have child-parent relationship?
That's where structured concurrency comes in. Here parents manages the children's.

This give us important guarantees around:

Life Time
Cancellation
Errors
Completion

We will start with simple concurrency tool async let

suppose we have:

func fetchUser() async -> String {
    return "Armaan"
}

func fetchPosts() async -> [String] {
    return ["Post 1", "Post 2"]
}

we can do it them sequentially

fetchUser
████████
↓
done
↓
fetchPosts
████████
↓
done

If each task takes 2 seconds then roughly it would take 4 seconds.
But these operations do not depend on each other.

We can run them concurrently.

async let user = fetchUser()
async let posts = fetchPosts()


let result = await(user, posts)

Now,

fetchUser
████████
↓
└──────── done

fetchPosts
████████
↓
└──────── done

They can make progress concurrently. If each takes roughly 2 seconds it would take approximately 2 seconds rather than 4 seconds.

How to Group and Display a List by Date in SwiftUI

Armaan Khan — Wed, 23 Sep 2026 11:21:57 +0000

Problem I Faced

I was working a gym Mac app for myself, I am new to SwiftUI and Apple ecosystem. I think I might be an almost year learning swift.

Till now I was just simply working on simple projects. Now I decided atleast I have to solve me daily problem.

I need to create an app for gym where I can track my progress.

While creating I got a Issue I want to fetch the workouts and show in the form of the list, but the problem was that I want to show the workouts that I have done according to the Dates.

How did I solved

I used Swift Data to store my data locally. It generally stores the data in the flat list. To show my all workout according to date I have to convert flat list into dictioinay.

1. Converting flat list into Dictionary

I created a Computed Property to convert the flat list into dictionary.

Dictionary(grouping: workouts) { ... } is a built-in Swift tool that walks through every item in workouts, one at a time, and asks the closure: "what key should this item live under?"

{ workout in Calendar.current.startOfDay(for: workout.date) }

It takes workout.date (which might be Sept 23, 9:03 AM) and strips the time off, giving just Sept 23, 12:00 AM. This is important — without this step, the 9am workout and the 6pm workout would be treated as different keys (since their exact timestamps differ), and they'd never end up grouped together.

2. Two ForEachs

Here, First ForEach shorts the items in the dictionary recent as first element.

Dictionaries have no built-in order in Swift, so if you looped over .keys directly, the dates could appear in any random order, and it might change every time. That's why .sorted(by: >) is there — it sorts the dates newest-first (> means descending).

groupedWorkouts[date] looks up the array of workouts belonging to that day.

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