【Swift/Combine】mapErrorメソッドの使い方！エラーを変換して流す方法

func mapError<E>(_ transform: @escaping (Self.Failure) -> E) -> Publishers.MapError<Self, E> where E : Error

struct DivisionByZeroError: Error {}
struct MyGenericError: Error { var wrappedError: Error }

/// 割り算をするメソッド
/// 0が渡された場合はエラーを投げる
func myDivide(_ dividend: Double, _ divisor: Double) throws -> Double {
    guard divisor != 0 else { throw DivisionByZeroError() }
    return dividend / divisor
}

let divisors: [Double] = [5, 4, 3, 2, 1, 0]
divisors.publisher
    .tryMap { try myDivide(1, $0) }
    .mapError { MyGenericError(wrappedError: $0) }
    .sink(
        receiveCompletion: { print ("completion: \($0)") },
        receiveValue: { print ("value: \($0)", terminator: " ") }
    )