Zip

What is zip in Combine?

The zip operator in Combine combines values from multiple publishers into pairs (tuples).
It waits for each publisher to emit a value before sending the combined result.

Think of it like pairing people in a three-legged race:

• Each person (publisher) needs a partner before they can start moving.
• If one publisher emits a value but the other hasn’t, it waits.
• Once both publishers emit, they move forward together.

zip waits for each publisher to emit a value before combining them into a single output.

🔗 Official Docs: Apple Documentation

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How zip Works

• Combines values from two or more publishers into a tuple.
• Waits for all publishers to emit a value before producing an output.
• Pairs values one-to-one (it doesn’t repeat values if one publisher emits more than the other).

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Example: Pairing News Headlines & Authors

import Combine
 
// 1. Create two publishers
let newsHeadlines = ["Swift 6 Released!", "Combine Improvements!", "iOS 18 Announced!"].publisher
let authors = ["Alice", "Bob"].publisher
 
// 2. Zip the publishers
let cancellable = newsHeadlines
    .zip(authors)
    .sink { headline, author in
        print("📰 \(headline) - by \(author)")
    }
 
(The third headline **is not printed** because `zip` only pairs **matching values**.)

Key Takeaways

• zip waits for all publishers to emit before sending combined values.
• Pairs values one-to-one, discarding extra emissions from faster publishers.
• Useful when data must be synchronized, such as matching requests and responses.