Augmented Code

LLDB print commands for debugging in Xcode

Post author By Toomas Vahter
Post date May 6, 2024

Whoever has used Xcode for debugging has heard about the po command. This command is used for printing object descriptions. Whatever we write after po gets compiled into actual code and is executed in the context where the debugger has stopped. This is done twice, first to get the expression result and then to get the object description. It is actually an alias for the expression command: expression --object-description -- myVariable.

In addition to po, there is also a p command what is an alias to expression myVariable. The main difference is that it compiles and runs the expression once, does a type resolution, and then prints the result.

The third option for printing variables is the v command what is an alias to the frame command. It reads values from memory, does a type resolution (multiple times if, for example, the expression accesses properties) and prints the result. The main difference is that it does not compile and run any code when evaluating the expression, which makes it quick to run.

Based on this knowledge, as a long time po user, I have changed my approach a bit when debugging in Xcode. I start with the v command since it is the quickest to run. If v command does not work, switching to p and then to po.

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags Swift, Xcode

iOS Swift

Initializing @MainActor type from a non-isolated context in Swift

Post author By Toomas Vahter
Post date April 22, 2024
1 Comment on Initializing @MainActor type from a non-isolated context in Swift

Recently I was in the middle of working on code where I wanted a type to require @MainActor since the type was an ObservaleObject and makes sense if it always publishes changes on the MainActor. The MainActor type needed to be created by another type which is not a MainActor. How to do it?

This does not work by default, since we are creating the MainActor type from a non-isolated context.

	final class ViewPresenter {
	init(dataObserver: DataObserver) {
	// Call to main actor-isolated initializer 'init(dataObserver:)' in a synchronous nonisolated context
	self.viewState = ViewState(dataObserver: dataObserver)
	}

	let viewState: ViewState
	}

	@MainActor final class ViewState: ObservableObject {
	let dataObserver: DataObserver

	init(dataObserver: DataObserver) {
	self.dataObserver = dataObserver
	}

	@Published private(set) var status: Status = .loading
	@Published private(set) var contacts: [Contact] = []
	}

view raw ViewState.swift hosted with ❤ by GitHub

OK, this does not work. But since the ViewState has a simple init then why not slap nonisolated on the init and therefore not requiring the init to be called on a MainActor. This leads to a warning: “Main actor-isolated property ‘dataObserver’ can not be mutated from a non-isolated context; this is an error in Swift 6”. After digging in Swift forums to understand the error, I learned that as soon as init assigns the dataObserver instance to the MainActor guarded property, then compiler considers that the type is owned by the MainActor now. Since init is nonisolated, compiler can’t ensure that the assigned instance is not mutated by the non-isolated context.

	final class ViewPresenter {
	init(dataObserver: DataObserver) {
	self.viewState = ViewState(dataObserver: dataObserver)
	}

	let viewState: ViewState
	}

	@MainActor final class ViewState: ObservableObject {
	let dataObserver: DataObserver

	nonisolated init(dataObserver: DataObserver) {
	// Main actor-isolated property 'dataObserver' can not be mutated
	// from a non-isolated context; this is an error in Swift 6
	self.dataObserver = dataObserver
	}

	@Published private(set) var status: Status = .loading
	@Published private(set) var contacts: [Contact] = []
	}

view raw ViewState.swift hosted with ❤ by GitHub

This warning can be fixed by making the DataObserver type to conform to Sendable protocol which tells the compiler that it is OK, if the instance is mutated from different contexts (of course we need to ensure that the type really is thread-safe before adding the conformance). In this particular case, making the type Sendable was not possible, and I really did not want to go to the land of @unchecked Sendable, so I continued my research. Moreover, having nonisolated init looked like something what does not look right anyway.

Finally, I realized that since the ViewState is @MainActor, then I could make the viewState property @MainActor as well and delay creating the instance until the property is accessed. Makes sense since if I want to access the ViewState and interact with it then I need to be on the MainActor anyway. If the property is lazy var and created using a closure, then we achieve what we want: force the instance creation to MainActor. Probably, code speaks itself more clearly.

	final class ViewPresenter {
	private let viewStateBuilder: @MainActor () -> ViewState

	init(dataObserver: DataObserver) {
	self.viewStateBuilder = { ViewState(dataObserver: dataObserver) }
	}

	@MainActor lazy var viewState: ViewState = viewStateBuilder()
	}

	@MainActor final class ViewState: ObservableObject {
	let dataObserver: DataObserver

	init(dataObserver: DataObserver) {
	self.dataObserver = dataObserver
	}

	@Published private(set) var status: Status = .loading
	@Published private(set) var contacts: [Contact] = []
	}

view raw ViewState.swift hosted with ❤ by GitHub

What I like is that I can keep one of the types fully @MainActor and still manage the creation from a non-isolated context. The downside is having lazy var and handling the closure.

If you want to try my apps, then grab one of the free offer codes for Silky Brew.

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Buy me a coffee

Tags async, iOS, MainActor, structured concurrency, Swift

Swift

Getting started with Benchmark package

Post author By Toomas Vahter
Post date April 8, 2024
1 Comment on Getting started with Benchmark package

There was a blog post on swift.org about a new Swift package called Benchmark at the end of the March. As the name speaks for itself, it is all about measuring the performance of the piece of a code. Since last time I wrote about Merging sorted arrays with duplicates in Swift then it would be useful to know what is the performance of that function.

The function under measurement is just about merging two sorted arrays in a way that it detects duplicates, where the duplicate detection is based on the id.

The function we are going to measure is part of a Swift package. Since Benchmark is a separate package, we’ll need to add a package dependency as the first step. It brings in a couple of additional dependencies as well.

.package(url: "https://github.com/ordo-one/package-benchmark", .upToNextMajor(from: "1.0.0")),

Interestingly, setting up a separate target for the package is really easy.

swift package --allow-writing-to-package-directory Benchmark init MyNewBenchmarkTarget

Which creates a separate target ready for running benchmarks.

swift package benchmark --target MyNewBenchmarkTarget

Before we run, let’s set it up to benchmark our function mentioned before. Firstly, we need to add a dependency to the generated part of the Package.swift. Since my example package has a target “PackageExampleBenchmark” which contains the function we want to measure, then it needs to be a dependency of the benchmark target.

package.targets += [
    .executableTarget(
        name: "MyNewBenchmarkTarget",
        dependencies: [
            .product(name: "Benchmark", package: "package-benchmark"),
            "PackageExampleBenchmark" // <-- added
        ],
        path: "Benchmarks/MyNewBenchmarkTarget",
        plugins: [
            .plugin(name: "BenchmarkPlugin", package: "package-benchmark")
        ]
    ),
]

import Benchmark
import Foundation
import PackageExampleBenchmark

let benchmarks = {
    let original = BenchmarkData.generate(count: 100000, offset: 0)
    let other = BenchmarkData.generate(count: 10, offset: 70000)

    Benchmark("SomeBenchmark") { benchmark in
        for _ in benchmark.scaledIterations {
            blackHole(original.mergeSorted(with: other, areInIncreasingOrder: { $0.date < $1.date }))
        }
    }
}

enum BenchmarkData {
    static let referenceDate = Date(timeIntervalSince1970: 1711282131)

    struct Item: Identifiable {
        let id: String
        let date: Date

    }

    static func generate(count: Int, offset: Int) -> [Item] {
        let ids = (0..<count)
            .map({ $0 + offset })
        return zip(ids.shuffled(), ids).map({
            Item(id: "\($0)",
                 date: Self.referenceDate.addingTimeInterval(TimeInterval($1)))
        })
    }
}

If we now run the benchmark, we’ll get this:

➜  PackageExampleBenchmark swift package benchmark --target MyNewBenchmarkTarget
Building for debugging...
[1/1] Write swift-version--58304C5D6DBC2206.txt
Build complete! (0.18s)
Building for debugging...
[1/1] Write swift-version--58304C5D6DBC2206.txt
Build complete! (0.35s)
Build complete!
Building BenchmarkTool in release mode...
Building benchmark targets in release mode for benchmark run...
Building MyNewBenchmarkTarget

==================
Running Benchmarks
==================

100% [------------------------------------------------------------] ETA: 00:00:00 | MyNewBenchmarkTarget:SomeBenchmark

=======================================================================================================
Baseline 'Current_run'
=======================================================================================================

Host 'MacBook-Air.lan' with 8 'arm64' processors with 24 GB memory, running:
Darwin Kernel Version 23.4.0: Wed Feb 21 21:51:37 PST 2024; root:xnu-10063.101.15~2/RELEASE_ARM64_T8112

====================
MyNewBenchmarkTarget
====================

SomeBenchmark
╒═══════════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                        │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞═══════════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Malloc (total) (K) *          │      60 │      60 │      60 │      60 │      60 │      60 │      60 │     178 │
├───────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ Memory (resident peak) (K)    │    9077 │    9871 │    9904 │    9912 │    9912 │    9912 │    9912 │     178 │
├───────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ Throughput (# / s) (#)        │     188 │     183 │     180 │     178 │     177 │     131 │     113 │     178 │
├───────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ Time (total CPU) (μs) *       │    5266 │    5423 │    5517 │    5542 │    5616 │    7598 │    8672 │     178 │
├───────────────────────────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ Time (wall clock) (μs) *      │    5333 │    5460 │    5562 │    5612 │    5648 │    7623 │    8819 │     178 │
╘═══════════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

Great, we’ll see how long does it take. In the example above we were merging an array of 10000 elements with an array of 100 where half of them are duplicates. All of this runs under a 1 ms which is an excellent result.

Only a single data point does not give us a full picture. What I would like to know is how does it run when we have 10, 100, 1000, 10000, 100000 elements in the existing array and what happens if we try to merge 10, 100, 1000, 10000, 100000 elements to it.

let benchmarks = {
    Benchmark.defaultConfiguration = .init(
        metrics: [.wallClock]
    )

    let counts = [10, 100, 1000, 10000, 100000]
    let arrays = counts.map({ BenchmarkData.generate(count: $0, offset: 0) })

    for (originalIndex, originalCount) in counts.enumerated() {
        for (incomingIndex, incomingCount) in counts.reversed().enumerated() {
            let originalData = BenchmarkData.generate(count: originalCount, offset: 0)
            let incomingData = BenchmarkData.generate(count: incomingCount, offset: 0)
            Benchmark("\(originalCount) < \(incomingCount)") { benchmark in
                for _ in benchmark.scaledIterations {
                    blackHole(originalData.mergeSorted(with: incomingData, areInIncreasingOrder: { $0.date < $1.date }))
                }
            }
        }
    }
}

10 < 10
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │      13 │      13 │      13 │      13 │      13 │      20 │      38 │   10000 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10 < 100
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │      61 │      61 │      61 │      61 │      64 │      85 │     102 │   10000 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10 < 1000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │     500 │     503 │     507 │     525 │     528 │     556 │     629 │    1948 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10 < 10000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    5292 │    5411 │    5444 │    5476 │    5562 │    6304 │    6349 │     183 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10 < 100000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      53 │      54 │      54 │      54 │      54 │      55 │      55 │      19 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100 < 10
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │      46 │      46 │      46 │      47 │      51 │     111 │    1464 │   10000 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100 < 100
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │     115 │     116 │     118 │     118 │     126 │     142 │     529 │    8343 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100 < 1000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │     543 │     545 │     552 │     568 │     571 │     587 │     677 │    1795 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100 < 10000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    5347 │    5444 │    5472 │    5509 │    5554 │    5693 │    5746 │     183 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100 < 100000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      51 │      51 │      52 │      52 │      52 │      52 │      52 │      20 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

1000 < 10
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │     372 │     384 │     386 │     404 │     409 │     419 │     467 │    2555 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

1000 < 100
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │     444 │     456 │     458 │     473 │     481 │     499 │     542 │    2157 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

1000 < 1000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    1144 │    1166 │    1176 │    1188 │    1202 │    1248 │    1307 │     849 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

1000 < 10000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    5648 │    5722 │    5743 │    5775 │    5833 │    5939 │    5951 │     174 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

1000 < 100000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      53 │      54 │      54 │      54 │      54 │      54 │      54 │      19 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10000 < 10
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    3962 │    4039 │    4057 │    4090 │    4119 │    4174 │    4270 │     247 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10000 < 100
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    3923 │    4028 │    4059 │    4104 │    4166 │    4502 │    5312 │     245 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10000 < 1000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (μs) * │    4671 │    4784 │    4813 │    4846 │    4887 │    4956 │    4995 │     208 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10000 < 10000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      10 │      10 │      10 │      10 │      10 │      10 │      10 │     100 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

10000 < 100000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      57 │      57 │      57 │      58 │      59 │      59 │      59 │      18 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100000 < 10
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      40 │      41 │      41 │      41 │      41 │      41 │      41 │      25 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100000 < 100
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      39 │      39 │      40 │      40 │      40 │      41 │      41 │      26 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100000 < 1000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      38 │      38 │      38 │      38 │      38 │      39 │      39 │      27 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100000 < 10000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │      50 │      51 │      51 │      51 │      51 │      51 │      51 │      20 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

100000 < 100000
╒══════════════════════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╤═════════╕
│ Metric                   │      p0 │     p25 │     p50 │     p75 │     p90 │     p99 │    p100 │ Samples │
╞══════════════════════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╪═════════╡
│ Time (wall clock) (ms) * │     110 │     110 │     110 │     111 │     111 │     112 │     112 │      10 │
╘══════════════════════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╧═════════╛

All in all, seems like I can be pretty happy with these results since merging 10000 elements to 10000 elements takes around 10 ms. Merging 100 elements on the other hand, takes around 0.5 ms.

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags benchmark, iOS, Swift, Swift Package, Xcode

Foundation iOS Swift

Merging sorted arrays with duplicates in Swift

Post author By Toomas Vahter
Post date March 25, 2024

The other day, I needed a way for merging sorted arrays containing structs. In addition, not just merging arrays, I also needed to handle duplicates. The duplicate handling needed to prioritize elements being inserted to the existing array. The case for that was adding an updated element to the existing array. In general, sounded like a leet code exercise, but something what I actually needed.

The fact that we are dealing with structs and need to take care of duplicates, then one way for that would be rebuilding the resulting array every time when merging new elements. Looping over existing elements allows doing the duplicate detection and in the end, we just need to loop over existing elements once and new elements twice (twice due to duplicates handling). Identification for elements are served by an id property. Since we’ll rebuild the resulting array we need a way to figure out how to sort elements, therefore, we can use a typical areInIncreasingOrder closure familiar from other sort related APIs. Since we discussed using id for identification, we require that Array elements conform to Identifiable protocol.

	extension RandomAccessCollection {
	func sortedMerged(
	with otherSorted: [Element],
	areInIncreasingOrder: (Element, Element) -> Bool
	) -> [Element] where Element: Identifiable {

view raw SortedMerged.swift hosted with ❤ by GitHub

This interface will allow us to detect duplicates and keep the resulting array sorted after inserting new elements.

The core of the function is looping over existing array and new/other elements and adding the smaller element to the resulting array. Then advancing the index of the existing array or the new/other elements array, depending on which was just inserted, to the resulting array. One of the requirements is that we should prefer elements from the new/other elements array. Therefore, each time we try to add an element from the existing array to the resulting array, we should check that this element is not present in the new/other elements array. Such lookup is easy to implement with a Set which contains ids of all the elements in the new elements array. If we put everything together, the function looks like this.

	extension RandomAccessCollection {
	func sortedMerged(
	with otherSorted: [Element],
	areInIncreasingOrder: (Element, Element) -> Bool
	) -> [Element] where Element: Identifiable {
	let otherIds = Set<Element.ID>(otherSorted.map(\.id))
	var result = [Element]()
	result.reserveCapacity(count + otherSorted.count)
	var currentIndex = startIndex
	var otherIndex = otherSorted.startIndex
	while currentIndex < endIndex, otherIndex < otherSorted.endIndex {
	if areInIncreasingOrder(self[currentIndex], otherSorted[otherIndex]) {
	// Prefer elements from the other collection over elements in the existing collection
	if !otherIds.contains(self[currentIndex].id) {
	result.append(self[currentIndex])
	}
	currentIndex = self.index(after: currentIndex)
	} else {
	result.append(otherSorted[otherIndex])
	otherIndex = otherSorted.index(after: otherIndex)
	}
	}
	// The other sorted array was exhausted, add remaining elements from the existing array
	while currentIndex < endIndex {
	// Prefer elements from the other collection over elements in the existing collection
	if !otherIds.contains(self[currentIndex].id) {
	result.append(self[currentIndex])
	}
	currentIndex = self.index(after: currentIndex)
	}
	// The existing sorted array was exhausted, add remaining elements from the other array
	if otherIndex < otherSorted.endIndex {
	result.append(contentsOf: otherSorted[otherIndex…])
	}
	return result
	}
	}

view raw SortedMerged.swift hosted with ❤ by GitHub

Here is an example of how to use it. The example involves inserting elements where some are duplicates, with one of the properties has changed.

	struct Item: Identifiable {
	let id: String
	let date: Date
	}

	let referenceDate = Date(timeIntervalSince1970: 1711282131)
	let original: [Item] = [
	Item(id: "1", date: referenceDate.addingTimeInterval(1.0)),
	Item(id: "2", date: referenceDate.addingTimeInterval(2.0)),
	Item(id: "3", date: referenceDate.addingTimeInterval(3.0)),
	Item(id: "4", date: referenceDate.addingTimeInterval(4.0)),
	Item(id: "5", date: referenceDate.addingTimeInterval(5.0)),
	]
	let other: [Item] = [
	Item(id: "3", date: referenceDate.addingTimeInterval(1.5)),
	Item(id: "7", date: referenceDate.addingTimeInterval(2.5)),
	Item(id: "4", date: referenceDate.addingTimeInterval(4.0)),
	Item(id: "5", date: referenceDate.addingTimeInterval(5.5)),
	Item(id: "6", date: referenceDate.addingTimeInterval(8.0)),
	]
	let result = original.sortedMerged(with: other, areInIncreasingOrder: { $0.date < $1.date })
	result.forEach { item in
	print("\(item.id) – \(item.date.timeIntervalSince(referenceDate))")
	}
	// 1 – 1.0
	// 3 – 1.5
	// 2 – 2.0
	// 7 – 2.5
	// 4 – 4.0
	// 5 – 5.5
	// 6 – 8.0

view raw SortedMerged.swift hosted with ❤ by GitHub

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags iOS, Swift

iOS Swift

Collection with opaque base collection in Swift

Post author By Toomas Vahter
Post date March 11, 2024

The other day I had an interesting small problem to solve. How to create a custom collection type which could have other kinds of collections as a base collection. The use-case for the collection is being a middle layer for data sources of different types. Another important requirement was that we want to avoid any expensive array allocations. Otherwise, we could just initialize these data source with Swift Array and call it a day. Moreover, base collections could even change during runtime, therefore the custom collection can’t reference any concrete types of the base collection using generics.

The high-level definition of the collection look like this: struct WrappedCollection<Element>: RandomAccessCollection.

After researching this and digging through Swift collection documentation without any great ideas, I suddenly realized that the solution was simpler than expected. If we can limit WrappedCollection’s Index type to Int (one of the required associated types), then the collection’s implementation becomes really short, since then we can benefit from RandomAccessCollection‘s default implementations for required functions and properties. This means, we just need to implement startIndex, endIndex and subscript for accessing an element at index. If it is just three properties and methods to implement, and we want to avoid exposing the type of the base collection, then we can use closures. Simple as that.

	struct WrappedCollection<Element>: RandomAccessCollection {
	typealias Index = Int

	var startIndex: Index { _startIndex() }
	var endIndex: Index { _endIndex() }

	subscript(position: Index) -> Element {
	_position(position)
	}

	init<BaseCollection>(_ baseCollection: BaseCollection) where BaseCollection: RandomAccessCollection, BaseCollection.Element == Element, BaseCollection.Index == Index {
	_position = { baseCollection[$0] }
	_startIndex = { baseCollection.startIndex }
	_endIndex = { baseCollection.endIndex }
	}

	private let _endIndex: () -> Index
	private let _startIndex: () -> Index
	private let _position: (Index) -> Element
	}

view raw WrappedCollection.swift hosted with ❤ by GitHub

Since the base collection is captured using closures, the base collection’s type can be anything as long as it follows some basic limits where the Index associated type is Int and the generic Element types match. In the end, we can create a property of the new type, which can change the base collection type in runtime. Here is an example:

	// Base collection is an Array
	private var items = WrappedCollection<Item>([Item(…), Item(…)])

	// Base collection is an OtherCustomCollection type
	func received(_ items: OtherCustomCollection<Item>) {
	self.items = WrappedCollection(items)
	}

view raw Example.swift hosted with ❤ by GitHub

Just to reiterate that this makes sense only when it is too expensive to initialize Swift Array with elements of other collection types. Most of the time it is OK, but if not, then we can use the approach presented in this post.

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags iOS, RandomAccessCollection, Swift

iOS Swift SwiftUI

Performing accessibility audits with UI tests on iOS

Post author By Toomas Vahter
Post date February 26, 2024

A new way how to test your app’s accessibility was added in iOS 17. XCUIApplication has a new method, performAccessibilityAudit. It has two arguments where the first is audit types which is by default set to all. The second argument is an issue handler, and we can use if for filtering out any false positives. Let’s see what are the different audit types. Audit types are listed under XCUIAccessibilityAuditType type: contrast, elementDetection, hitRegion, sufficientElementDescription, dynamicType, textClipped, and trait.

Since I recently released my app Silky Brew, then let’s see how to set up the accessibility auditing with UI-tests.

	final class AccessibilityAuditTests: XCTestCase {
	override func setUpWithError() throws {
	continueAfterFailure = false
	}

	func testBeansListAccessibility() throws {
	let app = XCUIApplication()
	app.launchEnvironment["SBOnboardingVisibility"] = "-1"
	app.launchEnvironment["SBSkipsAnimations"] = "1"
	app.launchEnvironment["SBUsesPreviewData"] = "1"
	app.launch()
	try app.performAccessibilityAudit()
	}
	}

view raw AccessibilityAudit.swift hosted with ❤ by GitHub

The test sets some environment keys which are used by the app to reconfigure some of its state. In the example above, we turn off onboarding view, speed up animations, and enable custom data (pre-defined user content). Here we can see how the test is running.

The accessibility audit did not come back without issues. One of the issues was a hitRegion problem. Report navigator shows more information about the failure.

After some trial and error, I found the issue triggering it. Not sure why, but the performAccessibilityAudit function failed to catch the element triggering the issue. Fortunately, accessibility indicator was able to pinpoint the element without a problem. So seems like if UI-tests catch accessibility issues but fail to highlight elements, then we can still go back to accessibility indicator for finding these. The particular issue was with the row view which shows several lines of text and two of these labels were using footnote and caption text styles. This in turn made text labels smaller and triggered the hitRegion error.

	VStack(alignment: .leading) {
	Text(beans.name)
	Text("by \(beans.roastery)")
	.font(.footnote)
	.foregroundStyle(.secondary)
	if let grindLabel {
	Divider()
	Text(grindLabel)
	.font(.caption)
	.foregroundStyle(.secondary)
	}
	}

view raw RowView.swift hosted with ❤ by GitHub

Since the row view is just multiple lines of text, then we can make it easier for accessibility users to read by combining all the text labels into one by adding .accessibilityElement(children: .combine) to the VStack. This solved that particular issue.

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags iOS, performAccessibilityAudit, Swift, SwiftUI

Swift SwiftUI

Opening hyperlinks in SwiftUI

Post author By Toomas Vahter
Post date February 12, 2024

Opening hyperlinks in UIKit with UILabel is unexpectedly complex, what about SwiftUI? In this post, we’ll dive into opening hyperlinks in SwiftUI.

If we just would like to show a hyperlink, then the best way is to the Link view. We can just feed it with a title and the destination URL. In addition, we can even apply a button style to it.

Link("Silky Brew", destination: AppConstants.URLs.silkyBrew)
  .buttonStyle(.borderedProminent)

By default, URLs are opened in the default web browser or if we are dealing with universal links, then in the appropriate app. If we have a desire to change how links are opened, we can apply a custom OpenURLAction. Here is an example how to open a URL in SFSafariViewController (SafariURL is just an Identifiable supported URL wrapper used for sheet’s binding and SafariView is SFSafariViewController wrapper with UIViewControllerRepresentable).

Link("Signal Path", destination: AppConstants.URLs.signalPath)
  .environment(\.openURL, OpenURLAction(handler: { url in
    safariURL = SafariURL(url: url)
    return .handled
}))
  .sheet(item: $safariURL, content: { safariURL in
    SafariView(url: safariURL.url) 
  })

Often we are dealing with a case where we have text which contains some links as well. In comparison to UIKit, it is way more simple. We can just use the Markdown syntax to define the link and that is all to it.

Text("Hello, world! Here is my [blog](https://augmentedcode.io/blog)")

If we would like to use a custom URL handler, then we can override the default handler through the openURL environment value. Can be handy to just have keys for URL in text and substituting these with actual URLs when handling the tap.

Text("Here are some apps: [Silky Brew](silky), [Signal Path](signal), and [Drifty Asteroid](drifty)")
                .environment(\.openURL, OpenURLAction(handler: { url in
                    switch url.absoluteString {
                    case "drifty": .systemAction(AppConstants.URLs.driftyAsteroid)
                    case "signal": .systemAction(AppConstants.URLs.signalPath)
                    case "silky": .systemAction(AppConstants.URLs.silkyBrew)
                    default: .systemAction
                    }
                }))

When talking about the OpenURLAction in greater detail, then the different return values are:

handled – handler took care of opening the URL (e.g. opening the URL in SFSafariViewController)
discarded – handler ignored the handling
systemAction – system handler opens the URL
systemAction(_:) – use a different URL (e.g. adding query parameters)

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags hyperlink, iOS, OpenURLAction, SFSafariViewController, Swift, URL

iOS Swift

Avoiding subtle mistake when guarding mutable state with DispatchQueue

Post author By Toomas Vahter
Post date January 29, 2024

Last week, I spent quite a bit of time on investigating an issue which sometimes happened, sometimes did not. There was quite a bit of code involved running on multiple threads, so tracking it down was not so simple. No surprise to find that this was a concurrency issue. The issue lied in the implementation of guarding a mutable state with DispatchQueue. The goal of the blog post is to remind us again a pattern which looks nice at first but actually can cause issues along the road.

Let’s have a look at an example where we have a Storage class which holds data in a dictionary where keys are IDs and values are Data instances. There are multiple ways for guarding the mutable state. In the example, we are using a concurrent DispatchQueue. Concurrent queues are not as optimized as serial queues, but the reasoning here is that we store large data blobs and concurrent reading gives us a slight benefit over serial reading. With concurrent queues we must make sure all the reading operations have finished before we mutate the shared state, and therefore we use the barrier flag which tells the queue to wait until all the enqueued tasks are finished.

	final class Storage {
	private let queue = DispatchQueue(label: "myexample", attributes: .concurrent)
	private var _contents = [String: Data]()

	private var contents: [String: Data] {
	get {
	queue.sync { _contents }
	}
	set {
	queue.async(flags: .barrier) { self._contents = newValue }
	}
	}

	func store(_ data: Data, forIdentifier id: String) {
	contents[id] = data
	}
	// …
	}

view raw Storage.swift hosted with ❤ by GitHub

The snippet above might look pretty nice at first, since all the logic around synchronization is in one place, and we can use the contents property in other functions without needing to think about using the queue. For validating that it works correctly, we can add a unit test.

	func testThreadSafety() throws {
	let iterations = 100
	let storage = Storage()
	DispatchQueue.concurrentPerform(iterations: iterations) { index in
	storage.store(Data(), forIdentifier: "\(index)")
	}
	XCTAssertEqual(storage.numberOfItems, iterations)
	}

view raw Test.swift hosted with ❤ by GitHub

The test fails because we actually have a problem in the Storage class. The problem is that contents[id] = data does two operations on the queue: firstly, reading the current state using the property getter and then setting the new modified dictionary with the setter. Let’s walk this through with an example where thread A calls the store function and tries to add a new key “d” and thread B calls the store function at the same time and tries to add a new key “e”. The flow might look something like this:

A calls the getter and gets an instance of the dictionary with keys “a, b, c”. Before the thread A calls the setter, thread B already had a chance to read the dictionary as well and gets the same keys “a, b, c”. Thread A reaches the point where it calls the setter and inserts modified dictionary with keys”a, b, c, d” and just after that the thread B does the same but tries to insert dictionary with keys “a, b, c, e”. When the queue ends processing all the work items, the key “d” is going to be lost, since the thread B managed to read the shared dictionary state before the thread A modified it. The morale of the story is that when modifying a shared state, we must make sure that reading the initial state and setting a new value must be synchronized and can’t happen as separate work items on the synchronizing queue. This happened here, since using the dictionaries subscript first runs the getter and then the setter.

The suggestion how to fix such issues is to use a single queue and making sure that read and write happen within the same work item.

	func store(_ data: Data, forIdentifier id: String) {
	// Incorrect because read and write happen in separate blocks on the queue
	// contents[id] = data

	// Correct
	queue.async(flags: .barrier) {
	self._contents[id] = data
	}
	}

view raw Fixed.swift hosted with ❤ by GitHub

An alternative approach to this Storage class’ implementation with new concurrency features in mind could be using the new actor type instead. But keep in mind that in that case we need to use await when accessing the storage since actors are part of the structured concurrency in Swift. Using the await keyword in turn requires having async context available, so it might not be straight-forward to adopt.

	actor Storage {
	private var contents = [String: Data]()

	func store(_ data: Data, forIdentifier id: String) {
	contents[id] = data
	}

	var numberOfItems: Int { contents.count }
	}

	// Example:
	// await storage.store(data, forIdentifier: id)

view raw Actor.swift hosted with ❤ by GitHub

If this was helpful, please let me know on Mastodon@toomasvahter or Twitter @toomasvahter. Feel free to subscribe to RSS feed. Thank you for reading.

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Tags async, await, barrier, concurrency, DispatchQueue, iOS, Swift

iOS Swift SwiftUI

SubscriptionStoreView for iOS apps

Post author By Toomas Vahter
Post date January 15, 2024

While building my indie iOS app, I decided to go for a subscription type of approach. At first, I built a fully custom upsell view which showed all the subscription options and handled the purchase actions (not as straight-forward as it sounds). Later, I realized that since iOS 17 there is a SubscriptionStoreView which does all of this and allows some customization as well. The aim of the blog post it to demonstrate how to configure the SubscriptionStoreView and therefore saving time by not building a fully custom one.

Configuring the testing environment for subscriptions

Before we start using the SubscriptionStoreView, we will need to configure subscriptions with Xcode’s StoreKit configuration file. This allows us to test subscriptions without needing to set everything up on the App Store. Open the new file panel and select StoreKit Configuration File. After that, create a subscription group and some auto-renewable subscriptions. In the example app, I just created a “Premium” subscription group and added “Monthly” and “Yearly” auto-renewable subscriptions.

The last thing to do is setting this configuration file as the StoreKit configuration file to the current scheme.

Using the SubscriptionStoreView for managing subscriptions

Now we are ready to go and display the SubscriptionStoreView. Since we are going to configure it a bit by inserting custom content into it, we’ll create a wrapping SubscriptionsView and use the StoreKit provided view from there. Let’s see an example first.

	struct SubscriptionsView: View {
	var body: some View {
	SubscriptionStoreView(productIDs: Subscriptions.subscriptionIDs) {
	VStack {
	VStack(spacing: 8) {
	Image(systemName: "graduationcap.fill")
	.resizable()
	.scaledToFill()
	.frame(width: 96, height: 96)
	.foregroundStyle(Color.brown)
	Text("Premium Access")
	.font(.largeTitle)
	Text("Unlock premium access for enabling X and Y.")
	.multilineTextAlignment(.center)
	}
	.padding()
	}
	}
	.subscriptionStorePolicyDestination(url: AppConstants.URLs.privacyPolicy, for: .privacyPolicy)
	.subscriptionStorePolicyDestination(url: AppConstants.URLs.termsOfUse, for: .termsOfService)
	.subscriptionStoreButtonLabel(.multiline)
	.storeButton(.visible, for: .restorePurchases)
	}
	}

view raw SubscriptionView.swift hosted with ❤ by GitHub

The view above is pretty much the minimal we need to get going. App review requires having terms of service and privacy policy visible and also the restore subscription button as well.

There is quite a bit of more customization of what we can do. Adding these view modifiers will give us a slightly different view.

	.subscriptionStorePolicyForegroundStyle(.teal)
	.subscriptionStoreControlStyle(.prominentPicker)
	.subscriptionStoreControlIcon { product, info in
	switch product.id {
	case "premium_yearly": Image(systemName: "star.fill").foregroundStyle(.yellow)
	default: EmptyView()
	}
	}
	.background {
	Color(red: 1.0, green: 1.0, blue: 0.95)
	.ignoresSafeArea()
	}

view raw SubscriptionView.swift hosted with ❤ by GitHub

Note: While playing around with subscriptions, an essential tool is in Xcode’s Debug > StoreKit > Manage Transactions menu.

Observing subscription changes

Our app also needs to react to subscription changes. StoreKit provides Transaction.currentEntitlements and Transaction.updates for figuring out the current state and receiving updates. A simple way for setting this up in SwiftUI is to create a class and inserting it into SwiftUI environment. On app launch, we can read the current entitlements and set up the observation for updates.

	@Observable final class Subscriptions {
	static let subscriptionIDs = ["premium_monthly", "premium_yearly"]

	// MARK: Starting the Subscription Observing

	@ObservationIgnored private var observerTask: Task<Void, Never>?

	func prepare() async {
	guard observerTask == nil else { return }
	observerTask = Task(priority: .background) {
	for await verificationResult in Transaction.updates {
	consumeVerificationResult(verificationResult)
	}
	}

	for await verificationResult in Transaction.currentEntitlements {
	consumeVerificationResult(verificationResult)
	}
	}

	// MARK: Validating Purchased Subscription Status

	private var verifiedActiveSubscriptionIDs = Set<String>()

	private func consumeVerificationResult(_ result: VerificationResult<Transaction>) {
	guard case .verified(let transaction) = result else {
	return
	}

	if transaction.revocationDate != nil {
	verifiedActiveSubscriptionIDs.remove(transaction.productID)
	}
	else if let expirationDate = transaction.expirationDate, expirationDate < Date.now {
	verifiedActiveSubscriptionIDs.remove(transaction.productID)
	}
	else if transaction.isUpgraded {
	verifiedActiveSubscriptionIDs.remove(transaction.productID)
	}
	else {
	verifiedActiveSubscriptionIDs.insert(transaction.productID)
	}
	}

	var hasPremium: Bool {
	!verifiedActiveSubscriptionIDs.isEmpty
	}
	}

view raw Subscriptions.swift hosted with ❤ by GitHub

Next, let’s insert it into the SwiftUI environment and update the current state. Wherever we need to read the state, we can access the Subscriptions class and read the hasPremium property. Moreover, thanks to the observation framework, the SwiftUI view will automatically update when the state changes.

	@main
	struct SwiftUISubscriptionStoreViewExampleApp: App {
	@State private var subscriptions = Subscriptions()

	var body: some Scene {
	WindowGroup {
	ContentView()
	.environment(subscriptions)
	.task {
	await subscriptions.prepare()
	}
	}
	}
	}

	struct ContentView: View {
	@Environment(Subscriptions.self) var subscriptions
	@State private var isPresentingSubscriptions = false

	var body: some View {
	VStack {
	Text(subscriptions.hasPremium ? "Subscribed!" : "Not subscribed")
	Button("Show Subscriptions") {
	isPresentingSubscriptions = true
	}
	}
	.sheet(isPresented: $isPresentingSubscriptions, content: {
	SubscriptionsView()
	})
	.padding()
	}
	}