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# Publishers.Reduce

A publisher that applies a closure to all received elements and produces an accumulated value when the upstream publisher finishes.

```
struct Reduce<Upstream, Output> where Upstream : Publisher
```

## Topics

### Creating a reduce publisher

[`init(upstream:initial:nextPartialResult:)`](/documentation/Combine/Publishers/Reduce/init(upstream:initial:nextPartialResult:))

Creates a publisher that applies a closure to all received elements and produces an accumulated value when the upstream publisher finishes.

### Declaring supporting types

[`Publishers.Output`](/documentation/Combine/Publishers/Output)

A publisher that publishes elements specified by a range in the sequence of published elements.

[`Publishers.Reduce.Failure`](/documentation/Combine/Publishers/Reduce/Failure)

The kind of errors this publisher might publish.

### Inspecting publisher properties

[`upstream`](/documentation/Combine/Publishers/Reduce/upstream)

The publisher from which this publisher receives elements.

[`initial`](/documentation/Combine/Publishers/Reduce/initial)

The initial value provided on the first invocation of the closure.

[`nextPartialResult`](/documentation/Combine/Publishers/Reduce/nextPartialResult)

A closure that takes the previously-accumulated value and the next element from the upstream publisher to produce a new value.


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