# `sov-default-stf`
### `AppTemplate`
This crate contains an implementation of a `StateTransitionFunction` called `AppTemplate` that is specifically designed to work with the Module System. The `AppTemplate` relies on a set of traits that, when combined, define the logic for transitioning the rollup state.
1. The `DispatchCall` trait is responsible for decoding serialized messages and forwarding them to the appropriate module.
1. The `Genesis` trait handles the initialization process of the rollup. It sets up the initial state upon the rollup deployment.
1. The `TxHooks` & `ApplyBlobHooks` traits that allow for the injection of custom logic into the transaction processing pipeline. They provide a mechanism to execute additional actions or perform specific operations during the transaction processing phase.
### `Runtime`
Both the `DispatchCall` and `Genesis` traits can be automatically derived (see `RT` in the above snippet) for any set of modules:
```rust ignore
#[derive(Genesis, DispatchCall, MessageCodec)]
#[serialization(borsh::BorshDeserialize, borsh::BorshSerialize)]
pub struct Runtime<C: Context> {
accounts: accounts::Accounts<C>,
bank: sov_bank::Bank<C>,
sequencer: sequencer::Sequencer<C>,
...
some other modules
}
```
The `Runtime` struct acts as the entry point where all the rollup modules are assembled together. The `#[derive]` macro generates the necessary implementations for the `Genesis and DispatchCall` traits from the `sov-module-api` crate.
To obtain an instance of the `StateTransitionFunction`, you can pass a`Runtime`, to the `AppTemplate::new(..)` method. This ensures that the implementation of the `StateTransitionFunction` is straightforward and does not require manual integration or complex setup steps.