temp_value being called during the read

[cjbissonnette]

I've got the following and am trying to use the temp_value to write out a sequence number during serialization:

#[deku(temp, temp_value="get_sequence()")]
sequence: u8,

It seems the temp_value is getting called during the de-serialization which I wouldn't expect. I would expect it to read the encoded value during the de-serialization, and use the temp_value when serializing.

Basically I have several spots in the protocol I want to read the value and use it as is during de-serialization, and provide some code during serialization. I know it could be achieved with update....but that has to be called manually with a mutable reference.

Is there any existing mechanism that would achieve this? I'm using 19.1.

[sharksforarms]

can you provide a minimal reproduction? this would help debug.

[cjbissonnette]

I'm sorry, I found my issue. I was calling To_bytes internally to calculate the CRC, but of course that is going to trigger the function, and the final to_bytes as the end will trigger it again. I'll have to think of a different way to accomplish this. Thanks for the reply, sorry for wasting your time.

I do have a feature request however. Would it be possible to add a flag such that the "update" function be called automatically if present before the serialization? I feel that would make that feature much more powerful.

[sharksforarms]

np!

Would it be possible to add a flag such that the "update" function be called automatically if present before the serialization?

yeah I wonder what could be done here. It's a trade-off, because as you previously noticed we need a &mut to update the value, which shouldn't be required for serialization. This is why it's explicit. A wrapper function around serialization could help here.

Another option is maybe some interior mutability type of setup, I haven't thought much about it as it feels anti-pattern'y

I agree likely most use cases would like to update on serialize, but this library doesn't want to make those assumptions and prefer flexibility