Chapters
Chapters

Chapters

Hide chapters

Combine: Asynchronous Programming With Swift

Fourth Edition · iOS 16 · Swift 5.8 · Xcode 14

Before You Begin

Section 0: 5 chapters
Show chapters Hide chapters

Section I: Introduction to Combine

Section 1: 2 chapters
Show chapters Hide chapters

Section II: Operators

Section 2: 6 chapters
Show chapters Hide chapters

Section III: Combine in Action

Section 3: 6 chapters
Show chapters Hide chapters

Section IV: Advanced Combine

Section 4: 5 chapters
Show chapters Hide chapters

Section V: Building a Complete App

Section 5: 2 chapters
Show chapters Hide chapters

6. Time Manipulation Operators
Written by Florent Pillet

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Heads up... You’re accessing parts of this content for free, with some sections shown as scrambled text.

Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now

Timing is everything. The core idea behind reactive programming is to model asynchronous event flow over time. In this respect, the Combine framework provides a range of operators that allow you to deal with time. In particular, how sequences react to and transform values over time.

As you’ll see throughout this chapter, managing the time dimension of your sequence of values is easy and straightforward. It’s one of the great benefits of using a framework like Combine.

Getting Started

To learn about time manipulation operators, you’ll practice with an animated Xcode Playground that visualizes how data flows over time. This chapter comes with a starter playground you’ll find in the projects folder.

The playground is divided into several pages. You’ll use each page to exercise one or more related operators. It also includes some ready-made classes, functions and sample data that’ll come in handy to build the examples.

If you have the playground set to show rendered markup, at the bottom of each page there will be a Next link that you can click to go to the next page.

Note: To toggle showing rendered markup on and off, select Editor ▸ Show Rendered/Raw Markup from the menu.

You can also select the page you want from the Project navigator in the left sidebar or even the jump bar at the top of the page. There are lots of ways to get around in Xcode!

Look at Xcode, and you’ll see the sidebar control at the top-left part of the window:

  1. Make sure the left sidebar button is toggled so you can see the list of Playground pages:

  1. Next, look at the top-right side of the window. You’ll see the view controls:

Show the editor with Live View. This will display a live view of the sequences you build in code. This is where the real action will happen!

  1. Showing the Debug area is important for most of the examples in this chapter. Toggle the Debug area using the following icon at the bottom-right of the window, or using the keyboard shortcut Command-Shift-Y:

Playground not Working?

From time to time Xcode may “act up” and not run properly your playground. If this happens to you, open the Preferences dialog in Xcode and select the Locations tab. Click the arrow next to the Derived Data location, depicted by the red circled 1 in the screenshot below. It shows the DerivedData folder in the Finder.

Shifting Time

Every now and again you need time traveling. While Combine can’t help with fixing your past relationship mistakes, it can freeze time for a little while to let you wait until self-cloning is available.

Collecting Values

In certain situations, you may need to collect values from a publisher at specified time intervals. This is a form of buffering that can be useful. For example, when you want to average a group of values over short periods of time and output the average.

Collecting Values (Part 2)

The second option the collect(_:options:) operator offers allows you to keep collecting values at regular intervals. It also allows you to limit the number of values collected.

Holding Off on Events

When coding user interfaces, you frequently deal with text fields. Wiring up text field contents to an action using Combine is a common task. For example, you may want to send a search URL request that returns a list of items matching what’s typed in the text field.

Debounce

Switch to the playground page named Debounce. Make sure that the Debug area is visible — View ▸ Debug Area ▸ Activate Console — so you can see the printouts of values debounce emits.

Throttle

The kind of holding-off pattern that debounce allows is so useful that Combine provides a close relative: throttle(for:scheduler:latest:). It’s very close to debounce, but the differences justify the need for two operators.

Timing Out

Next in this roundup of time manipulation operators is a special one: timeout. Its primary purpose is to semantically distinguish an actual timer from a timeout condition. Therefore, when a timeout operator fires, it either completes the publisher or emits an error you specify. In both cases, the publisher terminates.

Measuring Time

To complete this roundup of time manipulation operators, you’ll look at one particular operator which doesn’t manipulate time but just measures it. The measureInterval(using:) operator is your tool when you need to find out the time that elapsed between two consecutive values a publisher emitted.

Challenges

Challenge 1: Data

If time allows, you may want to try a little challenge to put this new knowledge to good use! Open the starter challenge playground in the projects/challenge folder. You see some code waiting for you:

Solution

You’ll find the solution to this challenge in the challenge/Final.playground Xcode playground. Here’s the solution code:

Key Points

In this chapter, you looked at time from a different perspective. In particular, you learned that:

Where to Go From Here?

This was a lot to learn. To put events in their right order, move along to the next chapter and learn about sequence operators!

5. Combining Operators
7. Sequence Operators
Have a technical question? Want to report a bug? You can ask questions and report bugs to the book authors in our official book forum here.
© 2026 Kodeco Inc.

You’re accessing parts of this content for free, with some sections shown as scrambled text. Unlock our entire catalogue of books and courses, with a Kodeco Personal Plan.

Unlock now