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Extension for a Combine-Publisher that returns the current and previous value.

 2 years ago
source link: https://gist.github.com/fxm90/be62335d987016c84d2f8b3731197c98
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fxm90 commented on May 17, 2021

Related test case:

class PairwiseTestCase: XCTestCase {

    func testPairwise() {
        // Given
        // We can't conform a tuple to `Equatable`, therefore we map the tuples to a struct.
        // We also can't define a struct in a protocol extension, therefore we used a `typealias` in the implementation.
        struct Pairwise<T: Equatable>: Equatable {
            let previous: T?
            let current: T
        }

        var receivedPairs = [Pairwise<Int>]()

        let range = 1 ... 5
        var subscriptions = Set<AnyCancellable>()

        // When
        range.publisher
            .pairwise()
            .sink {
                receivedPairs.append(Pairwise(previous: $0.previous, current: $0.current))
            }
            .store(in: &subscriptions)

        // Then
        XCTAssertEqual(receivedPairs, [
            Pairwise(previous: nil, current: 1),
            Pairwise(previous: 1, current: 2),
            Pairwise(previous: 2, current: 3),
            Pairwise(previous: 3, current: 4),
            Pairwise(previous: 4, current: 5),
        ])
    }
}

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