New to Rust: Seeking Clarification on RuntimeEvent Type Resolution in Substrate-Parachain-Template

Question

I'm a newcomer to Rust and have been working with the Substrate-Parachain-Template. So far, I've managed to get everything to compile and run without issue, which is a good start.

However, I've come across a part of the code that I'm struggling to understand, specifically the RuntimeEvent type resolution. Here's a snippet of the code in question:

impl pallet_nicks::Config for Runtime {
    .....
    // The ubiquitous event type.
    type Event = RuntimeEvent;
}

I'm confused about the RuntimeEvent type because there isn't an explicit import statement for it, and yet it doesn't seem to be causing any issues. It feels like magic, but I know that's not how programming works.

Could anyone kindly explain how Rust is resolving this type? I've checked the documentation but I couldn't find a clear explanation on this matter.

Any insight would be greatly appreciated. Thank you in advance!

Best Regards, AnonDao

Answer 1

In Rust, the associated types are types that are associated with a trait and defined within the trait itself or its implementing type. They allow traits to specify additional types that are relevant to their functionality.

In the context of the pallet_nicks::Config trait, the type Event is an associated type that represents the event type for that configuration. By declaring type Runtime = Runtime, it means that the type Runtime is being used as a self-reference or a way to refer to the overall runtime configuration itself. It allows the code within the pallet to work with and refer to the runtime configuration without needing to specify the exact type.

You can see read the docs here for understanding the runtime configurations and the you can check the impl of construct_runtime