Split tokens into a separate crate

[mversic]

We should explore ways how to move smart_contract/default/tokens.rs into a separate crate that can be imported by both iroha_executor and iroha_client. The big problem to consider here is how to have that crate swappable because we want, not just default tokens, but also user defined tokens to be provided by this crate.

The solution we find for tokens will be a foundation for creating executor_data_model crate which will contain all structures that are shared by iroha_executor and iroha_client such as custom expression system.

I somehow don't feel this is possible to do. I think that every executor will define it's own executor_data_model crate which will then be imported by the client. When a user creates their own executor, they will also make their own executor_data_model which can (but doesn't have to) re-export iroha_default_executor_data_model

[mversic]

so in essence we can define iroha_default_executor_data_model but users of iroha will have to define their own data model crates

[Arjentix]

I also think that would be the best approach.

Just the last note I have in mind.
Currently tokens are stored in the iroha_executor crate, not iroha_default_executor. I think we want to affiliate them with iroha_default_executor now, so iroha_default_executor_data_model sounds good to me.

[0x009922]

I have a concern about swappable data model in general. Currently, probably the main reason to use an SDK is to safely build data model types. If data model is not static, then Iroha users (other devs) will have to build their own SDKs, which seems like a huge overhead.

Not entirely sure if my concern is 100% related to this issue.

[mversic]

Not entirely sure if my concern is 100% related to this issue.

Yes, your concern is related and valid

[Arjentix]

Regarding SDK problem I think we should provide support for default types as we do now. But if users will decide that they need some kind of expressions or anything else they should be able to combine our SDK and their own data model

[mversic]

closed as part of #4791