---
title: "combineLatest(_:_:_:_:)"
framework: combine
role: symbol
role_heading: Instance Method
path: "combine/publisher/combinelatest(_:_:_:_:)"
---

# combineLatest(_:_:_:_:)

Subscribes to three additional publishers and invokes a closure upon receiving output from any of the publishers.

## Declaration

```swift
func combineLatest<P, Q, R, T>(_ publisher1: P, _ publisher2: Q, _ publisher3: R, _ transform: @escaping (Self.Output, P.Output, Q.Output, R.Output) -> T) -> Publishers.Map<Publishers.CombineLatest4<Self, P, Q, R>, T> where P : Publisher, Q : Publisher, R : Publisher, Self.Failure == P.Failure, P.Failure == Q.Failure, Q.Failure == R.Failure
```

## Parameters

- `publisher1`: A second publisher to combine with the first publisher.
- `publisher2`: A third publisher to combine with the first publisher.
- `publisher3`: A fourth publisher to combine with the first publisher.
- `transform`: A closure that receives the most-recent value from each publisher and returns a new value to publish.

## Return Value

Return Value A publisher that receives and combines elements from this publisher and three other publishers.

## Discussion

Discussion Use combineLatest(_:_:_:_:) when you need to combine the current and 3 additional publishers and transform the values using a closure in which you specify the published elements, to publish a new element. tip: The combined publisher doesn’t produce elements until each of its upstream publishers publishes at least one element. The combined publisher passes through any requests to all upstream publishers. However, it still obeys the demand-fulfilling rule of only sending the request amount downstream. If the demand isn’t unlimited, it drops values from upstream publishers. It implements this by using a buffer size of 1 for each upstream, and holds the most-recent value in each buffer. All upstream publishers need to finish for this publisher to finish. If an upstream publisher never publishes a value, this publisher never finishes. In the example below, as combineLatest(_:_:_:_:) receives the most-recent values published by four publishers, multiplies them together, and republishes the result: let pub = PassthroughSubject<Int, Never>() let pub2 = PassthroughSubject<Int, Never>() let pub3 = PassthroughSubject<Int, Never>() let pub4 = PassthroughSubject<Int, Never>()

cancellable = pub     .combineLatest(pub2, pub3, pub4) { firstValue, secondValue, thirdValue, fourthValue in         return firstValue * secondValue * thirdValue * fourthValue     }     .sink { print("Result: \($0).") }

pub.send(1) pub.send(2) pub2.send(2) pub3.send(9) pub4.send(1)

pub.send(3) pub2.send(12) pub.send(13) pub3.send(19)

// Prints: //  Result: 36.     // pub = 2,  pub2 = 2,   pub3 = 9,  pub4 = 1 //  Result: 54.     // pub = 3,  pub2 = 2,   pub3 = 9,  pub4 = 1 //  Result: 324.    // pub = 3,  pub2 = 12,  pub3 = 9,  pub4 = 1 //  Result: 1404.   // pub = 13, pub2 = 12,  pub3 = 9,  pub4 = 1 //  Result: 2964.   // pub = 13, pub2 = 12,  pub3 = 19, pub4 = 1

## See Also

### Collecting and republishing the latest elements from multiple publishers

- [combineLatest(_:_:)](combine/publisher/combinelatest(_:_:)-1n30g.md)
- [combineLatest(_:)](combine/publisher/combinelatest(_:).md)
- [combineLatest(_:_:_:)](combine/publisher/combinelatest(_:_:_:)-6ekpz.md)
- [combineLatest(_:_:)](combine/publisher/combinelatest(_:_:)-5crqg.md)
- [combineLatest(_:_:_:)](combine/publisher/combinelatest(_:_:_:)-48buc.md)