Combine Latest

What is combineLatest in Combine?

The combineLatest operator in Combine merges values from multiple publishers
and emits a new combined value whenever any publisher updates.

Think of it like a live news panel:

• Whenever a new headline or new expert opinion comes in, the panel updates.
• You always see the latest headline and the latest expert opinion together.
• If one source updates, the other keeps its most recent value.

combineLatest emits a new value whenever any of its publishers emits.

🔗 Official Docs: Apple Documentation

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How combineLatest Works

• Starts when all publishers have emitted at least one value.
• Whenever any publisher emits a new value, the latest values from all publishers are combined and sent.
• Always uses the latest values available from each publisher.

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Example: Live News Updates

import Combine
 
// 1. Create two publishers
let newsHeadlines = PassthroughSubject<String, Never>()
let expertOpinions = PassthroughSubject<String, Never>()
 
// 2. Combine the latest values
let cancellable = newsHeadlines
    .combineLatest(expertOpinions)
    .sink { headline, opinion in
        print("📰 \(headline) | 💬 Expert: \(opinion)")
    }
 
// 3. Send values (order matters)
newsHeadlines.send("Swift 6 Released!")  // Won't print yet (needs both values)
expertOpinions.send("Game changer!")     // ✅ Prints
newsHeadlines.send("Combine Improvements!") // ✅ Prints
expertOpinions.send("Developers will love it!") // ✅ Prints
 

Key Takeaways

• Starts after all publishers emit at least one value.
• Emits a new combined value every time any publisher updates.
• Always holds the latest value from each publisher.
• Useful for UI bindings, real-time data, and state management.