Derive Macro Upgradeable 

#[derive(Upgradeable)]

1. Derives Upgradeable a) implements the interface; requires only the auth to be defined b) sets wasm version by taking the version from Cargo.toml

2. Derives UpgradeableMigratable when both an upgrade and a migration are needed a) implements the interface; requires the auth and the migration logic to be defined b) sets wasm version by taking the version from Cargo.toml

Example for upgrade only:

#[derive(Upgradeable)]
#[contract]
pub struct ExampleContract;

impl UpgradeableInternal for ExampleContract {
    fn _require_auth(e: &Env, operator: &Address) {
        operator.require_auth();
        let owner = e.storage().instance().get::<_, Address>(&OWNER).unwrap();
        if *operator != owner {
            panic_with_error!(e, ExampleContractError::Unauthorized)
        }
    }
}

Example for upgrade and migration:

#[contracttype]
pub struct Data {
    pub num1: u32,
    pub num2: u32,
}

#[derive(UpgradeableMigratable)]
#[contract]
pub struct ExampleContract;


impl UpgradeableMigratableInternal for ExampleContract {
    type MigrationData = Data;

    fn _require_auth(e: &Env, operator: &Address) {
        operator.require_auth();
        let owner = e.storage().instance().get::<_, Address>(&OWNER).unwrap();
        if *operator != owner {
            panic_with_error!(e, ExampleContractError::Unauthorized)
        }
    }

    fn _migrate(e: &Env, data: &Self::MigrationData) {
        e.storage().instance().set(&DATA_KEY, data);
    }
}