Rust/Motoko/Azle CDK features

As part of Azle’s next release, I’m trying to compare the features of the Rust CDK, Motoko, and Azle. Here’s the documentation I have so far: GitHub - demergent-labs/azle at 431_feature_parity_documentation

I’m at a loss for understanding if some lower-level features are exposed by Motoko. Can someone help me out here? I’ve linked to the main section of missing feature documentation above, the question marks indicate what I don’t know. I’ll list them here as well.

My main question is if the following features from the Rust CDK are exposed in Motoko:

  1. arg data
  2. arg data raw
  3. arg data size
  4. notify
  5. notify raw
  6. notify with payment 128 (if notify is supported this is probably supported with normal cycles addition to the next call)
  7. reject
  8. reject code
  9. reject message
  10. reply
  11. reply raw
  12. result
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By design, none of these are exposed directly in Motoko but the System API equivalents are used in the implementations of Motoko’s higher-level abstractions.

1-3 is shared function argument binding.
4-6 is calling a Candid oneway function with or with cycles.
7-9 is exit via uncaught throw from a shared function
10-11 is exit via return (explicit or implicit) from a shared function.
12 is shared function call result handling, I guess, which is rolled into Motoko’s await, continuing on success or implicitly throwing an error on failure.

It looks like notify lets you call a non-oneway function as oneway, whether declared oneway or not in Candid. Motoko does not support this directly (but I think it can be achieved via a cast).

Rust lets you bypass Candid. Motoko does not, except for supporting raw calls, sending an receiving raw binary data (possibly non-Candid).

Rusts lets you declare non-Candid function/entrypoints. Motoko does not.


An enterprising Motoko dev could code up an example of each and it would make a great addition to some documentation/tutorials somewhere. It would be a really great way to understand how the IC works.

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