[rfc] [style] define generics with single characters when possible

[merklefruit]

Generics on struct should when possible use a single letter. Example:

pub struct ExecutionClient<C, P> {
	provider: DefaultProvider,
	chain: PhantomData<C>,
	pubsub: PhantomData<P>
}

instead of:

pub struct ExecutionClient<CHAIN, PUBSUB> {
	provider: DefaultProvider,
	chain: PhantomData<CHAIN>,
	pubsub: PhantomData<PUBSUB>
}

If two generics have semantics that make them hard to distinguish with a single letter, then we should use two letters to disambiguate.
For instance, a struct with a Provider and PubSub generics could become P and PS or similar. There is no strict rule here, but the guideline is to use identifiers that are short yet clear.

[thedevbirb]

I'm a bit on the fence about this. While on struct definition using short letters is fine, because the generics is used immediately and bounded to a descriptive field name, in impl blocks the context is lost.

Consider an impl block for ExecutionClient:

impl<C, P> ExecutionClient<C, P> { /* ... */ }

Now you have these two apparently meaningless letters, unless you have your struct definition close to your eyes.

At the same time having the generic written in screaming caps lock is a no-go. Perhaps a middle ground would be to write it as follows:

pub struct ExecutionClient<Chain, Pubsub> {
	provider: DefaultProvider,
	chain: PhantomData<Chain>,
	pubsub: PhantomData<Pubsub>
}

This pattern is also quite common in other languages like TypeScript.