tryAllSatisfy(_:)

Publishes a single Boolean value that indicates whether all received elements pass a given error-throwing predicate.

Declaration

func tryAllSatisfy(_ predicate: @escaping (Self.Output) throws -> Bool) -> Publishers.TryAllSatisfy<Self>

Parameters

predicate:
A closure that evaluates each received element. Return true to continue, or false to cancel the upstream and complete. The closure may throw an error, in which case the publisher cancels the upstream publisher and fails with the thrown error.

Return Value

A publisher that publishes a Boolean value that indicates whether all received elements pass a given predicate.

Discussion

Use the tryAllSatisfy(_:) operator to determine if all elements in a stream satisfy a criteria in an error-throwing predicate you provide. When this publisher receives an element, it runs the predicate against the element. If the predicate returns false, the publisher produces a false value and finishes. If the upstream publisher finishes normally, this publisher produces a true value and finishes. If the predicate throws an error, the publisher fails and passes the error to its downstream subscriber.

In the example below, an error-throwing predicate tests if each of an integer array publisher’s elements fall into the targetRange; the predicate throws an error if an element is zero and terminates the stream.

let targetRange = (-1...100)
let numbers = [-1, 10, 5, 0]

numbers.publisher
    .tryAllSatisfy { anInt in
        guard anInt != 0 else { throw RangeError() }
        return targetRange.contains(anInt)
    }
    .sink(
        receiveCompletion: { print ("completion: \($0)") },
        receiveValue: { print ("value: \($0)") }
    )

// Prints: "completion: failure(RangeError())"

With operators similar to reduce(_:_:), this publisher produces at most one value.