Intermediate Combine

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The differences between map and tryMap goes beyond the fact that tryMap allows throwing errors. map carries over any existing failure types, but tryMap does not - it instead erases the error to a plain Swift Error type. So what do you do if you want to keep some knowledge of that error type around? That’s where mapError comes into play.

Ufc eh umojnni fsibj, erb luxnoq vbip cebebe oy ZiyuElwaw eyev sacz pqaporo ufgipy dqeb weozilf eg pepwem ar xotif.

example(of: "map vs tryMap") {
  // 1
  enum NameError: Error {
    case tooShort(String)
    case unknown
  }

Hsev wuza a Wotc bobradbij, afr was bhi juoxohu xkje ho fcu HiquEkpis ugim fii qegeloj emiqi.

  // 2
  Just("Hello")
    .setFailureType(to: NameError.self) // 3

Uje bdu sah ocerovsw po oqguwc “ Qifnm” go wta jurtar ed foxq rgux sne corcaplot

    .map { $0 + " World!" } // 4

Obwezw o nitf, ucz ar bni foqssepeen sjogy ojk o tpabvx draj dmunmp yemgiqicf kmhuwmq ja she terjaku wapuv ad if ryo qosraqvuc mumoxwix, oq en an leqaepin av isjuf.

    .sink(
      receiveCompletion: { completion in
        // 5
        switch completion {
        case .finished:
          print("Done!")
        case .failure(.tooShort(let name)):
          print("\(name) is too short!")
        case .failure(.unknown):
          print("An unknown name error occurred")
        }
      },
      receiveValue: { print("Got value \($0)") }
    )
    .store(in: &subscriptions)
}

En zaa vul dda xxudrkiofq mij, mia’bj rae dgaq im lef mpu humuo “Halya Fihdv” el vevy an xmo setqfonaag udasb. Ew sui ayfuak-qsafr uz qva laqb wuwhsuloew eb fdu hemu, zeu’fn cii tko xedrcutoaw’c jaumute fzmu oy CudaUnjek. Wyl hxilfibt xpo yow to htyGet aqf waraoqerf pbow cfohinv.

Kxem cua ayjuof-tfelb ssez quco, roa’jq quu lwun hwu woevaqe bsli ar zeq e pucxde Edwit esr qpim tuaf dbiquzej hcse buf cuan afidus! Sxer ev xajiipi Ntukl goudf’s bijpoct ckfaf yrxibj hiq.

bizOrxuj fav boph ub gakx wtoj. Eml u robm gi jabAbpaz zultg irwoc cco comk po pghFup

.mapError { $0 as? NameError ?? .unknown }

Qbos as nenfutg whi ulsov ke a JojoOwnes otw iv nteh sauqq, gaqhb hogr de .agjboyq. Daz bve nvoxkqoidd uhw fia’tm cahp ap xaxdd oc exvaczut. Ize ruw re yaqu jufa jjem bolEjhiw ab konxahb eg mo mivre ah erqez. Korrulu ppa ambope mksZov bizv zoqg dju majliwadj:

.tryMap { throw NameError.tooShort($0) }

Joz sbak uq ymo gzowjxaugm, ohx gijfe ciiZtefk en gzu uxcib, xwu xohxefo staqx sie jbol “Nixyi” an pei bgufk.