Native token

Different blockchains come with different implementations of their native tokens. Odra wraps it all for you in easy-to-use code. Let's write a simple example of a public wallet - a contract where anyone can deposit their funds and anyone can withdraw them:

examples/src/features/native_token.rs

use odra::prelude::*;
use odra::{casper_types::U512, module::Module};

#[odra::module]
pub struct PublicWallet;

#[odra::module]
impl PublicWallet {
    #[odra(payable)]
    pub fn deposit(&mut self) {}

    pub fn withdraw(&mut self, amount: &U512) {
        self.env().transfer_tokens(&self.env().caller(), amount);
    }
}

danger

The code above works, but is dangerous and unfinished - besides allowing you to lose your funds to anyone, it doesn't make any checks. To keep the code simple, we skipped the part, where the contract checks if the transfer is even possible.

To see a more reasonable example, check out examples/src/contracts/tlw.rs in the odra main repository.

You can see a new attribute used here: #[odra(payable)] - it will add all the code needed for a function to be able to receive the funds. Additionally, we are using a new function from ContractEnv::transfer_tokens(). It does exactly what you are expecting it to do - it transfers native tokens from the contract to the specified address.

Testing

To be able to test how many tokens a contract (or any address) has, HostEnv comes with a function - balance_of:

examples/src/features/native_token.rs

#[cfg(test)]
mod tests {
    use super::PublicWalletHostRef;
    use odra::{casper_types::U512, host::{Deployer, HostRef, NoArgs}};

    #[test]
    fn test_modules() {
        let test_env = odra_test::env();
        let mut my_contract = PublicWalletHostRef::deploy(&test_env, NoArgs);
        assert_eq!(test_env.balance_of(my_contract.address()), U512::zero());

        my_contract.with_tokens(U512::from(100)).deposit();
        assert_eq!(test_env.balance_of(my_contract.address()), U512::from(100));

        my_contract.withdraw(U512::from(25));
        assert_eq!(test_env.balance_of(my_contract.address()), U512::from(75));
    }
}