Motoko Serialization

[mbeekman]

As a closer to this subject … the from_candid method returns an optional type or () (?Type) … this was a new thing for me, as it will not compile if you take that value and try to use it … so we need a switch to check whether it worked … even though it will assert if the “from_candid” fails … here is a quick code example that may prove useful to the next Explorer walking this path:

var tempBlobReturned : ?ArchiveType = from_candid(tempBlob); 

switch tempBlobReturned {
  case (?val) {
    Debug.print("RESTORE SUCCESS - have a value" ) ;
    tempArchiveRestored:=val ;
  };
  case null {
    Debug.print("RESTORE FAILED - have no value " ) ;
  };
};// end switch

Happy to respond if anything does not make sense here … extrapolated this solution from the following post:

Сannot producer expected type

You need to switch and pattern-match on the optional value: switch result { case (?val) { .../* val : Text here*/... }; case null { ... }; } If you have multiple of such tests, take a look at the do? construct, which comes in handy and e.g. allows collapsing multiple switches into one: let result = do? { List.last(list1)! + List.last(list2)! + 1 }; switch result { case (?n) { ... handle result ... } case null { ... handle error ... } } The ! operator inside a do? block converts ?T t…

needless to say, but very obtuse … thanks @rossberg …
please rock on …