Modules

Simply put, modules in Odra let you reuse your code between contracts or even projects. Every contract you write is also a module, thanks to the #[odra::module] attribute. This means that we can easily rewrite our math example from the previous article, to use a single contract, but still separate our "math" code:

examples/src/features/modules.rs

use crate::features::cross_calls::MathEngine;
use odra::module::SubModule;
use odra::prelude::*;

#[odra::module]
pub struct ModulesContract {
    pub math_engine: SubModule<MathEngine>
}

#[odra::module]
impl ModulesContract {
    pub fn add_using_module(&self) -> u32 {
        self.math_engine.add(3, 5)
    }
}

info

To use a module as a component of another module, you need to use the SubModule type. This is a special type that crates a keyspace (read more in Storage Layout) and provide access to its public methods.

Note that we didn't need to rewrite the MathEngine - we are using the contract from cross calls example as a module!

info

To see how modules can be used in a real-world scenario, check out the OwnedToken example in the main Odra repository!

Testing

As we don't need to hold addresses, the test is really simple:

examples/src/features/modules.rs

#[cfg(test)]
mod tests {
    use super::ModulesContractHostRef;
    use odra::host::{Deployer, NoArgs};

    #[test]
    fn test_modules() {
        let test_env = odra_test::env();
        let modules_contract = ModulesContractHostRef::deploy(&test_env, NoArgs);
        assert_eq!(modules_contract.add_using_module(), 8);
    }
}

What's next

We will see how to handle native token transfers.