# ControlNotificationStream.prefix(while:)

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

```
ControlNotificationStream.prefix(while:)(while: (Self.Element) async -> Bool) -> AsyncPrefixWhileSequence<Self>
```

Returns an asynchronous sequence, containing the initial, consecutive elements of the base sequence that satisfy the given predicate.

Use `prefix(while:)` to produce values while elements from the base
sequence meet a condition you specify. The modified sequence ends when
the predicate closure returns `false`.

In this example, an asynchronous sequence called `Counter` produces `Int`
values from `1` to `10`. The `prefix(while:)` method causes the modified
sequence to pass along values so long as they aren’t divisible by `2` and
`3`. Upon reaching `6`, the sequence ends:

    let stream = Counter(howHigh: 10)
        .prefix { $0 % 2 != 0 || $0 % 3 != 0 }
    for try await number in stream {
        print(number, terminator: " ")
    }
    // Prints "1 2 3 4 5 "
    
- Parameter predicate: A closure that takes an element as a parameter and
  returns a Boolean value indicating whether the element should be
  included in the modified sequence.
- Returns: An asynchronous sequence of the initial, consecutive
  elements that satisfy `predicate`.