Initialize a struct from data, dictionary etc

InitStructFromData.swift

// Credit: https://stackoverflow.com/users/887210/colgraff
struct Header {
      let version : UInt
      let options : UInt
      let records : UInt
    }

    // adds marshaling
    extension Header {
      enum Keys: String { case version, options, records }

      init?(settings: [Keys:Any]) {
        guard
          let version = settings[.version] as? UInt,
          let marshalled = Header.marshal(version: version)(settings)
          else { return nil }
        self = marshalled
      }
      
      // Execute marshalling
      static func marshal(version: UInt) -> ([Keys:Any]) -> Header? {
        switch version {
        case 0: return marshal0
        default: return { (_) -> Header? in return nil } // no match, by default returns a `nil`
        }
      }
      
      // Version 0 marshaling
      static private var marshal0: (([Keys:Any]) -> Header?) = { (settings) -> Header? in
        guard let version = settings[.version] as? UInt else { return nil }
        guard let options = settings[.options] as? UInt else { return nil }
        guard let records = settings[.records] as? UInt else { return nil }
        return Header(version: version, options: options, records: records)
      }
    }

    let data: [Header.Keys: UInt] = [.version: 0, .options: 5, .records: 121]

    if let foo = Header(settings: data) {
      print(foo) // Header(version: 5, options: 5, records: 121)
    }

I simplified the logic a bit by moving the version check into the marshal method. Take a look at my fork.