Introduction

What Combine is for, and what has replaced most of it

Combine is Apple’s framework for values that arrive over time: a network response, a text field’s contents, a notification, the tick of a timer. Instead of a callback per source, every source becomes a Publisher, and publishers compose.

let cancellable = NotificationCenter.default
    .publisher(for: UITextField.textDidChangeNotification)
    .compactMap { ($0.object as? UITextField)?.text }
    .debounce(for: .milliseconds(300), scheduler: RunLoop.main)
    .removeDuplicates()
    .sink { query in search(query) }

Four operators replace a debounce timer, a “did it change?” check and a delegate.

Warning

Much of what Combine was written for is now in the language. async/await covers one-shot work better than Future, and AsyncSequence covers streams with less machinery. Reach for Combine when you genuinely need its operator vocabulary — merging, combining latest values, backpressure — not out of habit.

What this book covers

This is a template chapter. The full text is still being written.