# ControlNotificationStream.reduce(into:_:)

- **Module:** ControlNotificationStream
- **Package:** libtmux-swift
- **Language:** Swift
- **Kind:** method
- **Page:** https://libtmux.org/reference/swift/controlnotificationstream-reduce(into-_-)/

```
ControlNotificationStream.reduce(into:_:)(into: Result, updateAccumulatingResult: (inout Result, Self.Element) async throws -> Void) -> Result
```

Returns the result of combining the elements of the asynchronous sequence using the given closure, given a mutable initial value.

Use the `reduce(into:_:)` method to produce a single value from the
elements of an entire sequence. For example, you can use this method on a
sequence of numbers to find their sum or product.

The `updateAccumulatingResult` closure executes sequentially with an
accumulating value initialized to `initialResult` and each element of the
sequence.

Prefer this method over `reduce(_:_:)` for efficiency when the result is
a copy-on-write type, for example an `Array` or `Dictionary`.

- Parameters:
  - initialResult: The value to use as the initial accumulating value.
    The `nextPartialResult` closure receives `initialResult` the first
    time the closure executes.
  - updateAccumulatingResult: A closure that combines an accumulating
    value and an element of the asynchronous sequence into a new
    accumulating value, for use in the next call of the
    `nextPartialResult` closure or returned to the caller.
- Returns: The final accumulated value. If the sequence has no elements,
  the result is `initialResult`.

## Raises

- `Void`