Importing blob from canister

[FloorLamp]

Hi all! Hope everything has been going well, I've recently started building stuff with the SDK again and had a quick question.

I have two files:

// B.mo
actor B {
  public func get(): async Blob { "Hello" };
}

// A.mo
import B "canister:B";

type A = actor {
  get: () -> async Blob;
};

actor {
  let a: A = B;
}

This produces an error:

type error, expression of type
  actor {get : shared () -> async [Nat8]}
cannot produce expected type
  actor {get : shared () -> async Blob}

Is this expected? I can change A to use [Nat8], but I'm trying to keep the types the same. Thanks!

[nomeata]

Yes, that is somewhat expected; in the Candid IDL (https://github.com/dfinity/candid/blob/master/IDL.md) blob and vec nat8 are aliases. I think there is work towards making that less annoying for blob (i.e. import it into motoko as Blob again), but in general this problem is unavoidable, and will surface with other types.

You can just write A.mo using Blob, but then you don’t get to use the nice type import feature…

[chenyan-dfinity]

This is a bug, we have a PR to fix this in the compiler. The expected behavior is to import as a Blob type if the candid file says blob.