Enhancements for swift-dependencies documentation

[evilhonda3030]

Hi there,

I recently discovered some advanced topics about swift-dependencies library in its documentation. There was a lot of information about how we can override dependencies for the certain places in our codebase which was followed by dos and donts examples. Especially there were some examples on how we can propagate overriden dependencies deeper to child features.

However, I see that documentation could have one more on dependencies propagation when it comes to using this library in a TCA environment. Basically this example is about how not to make mistakes when working with an implementation of the Reducer protocol.

It comes down to not forgetting do this when fulfilling body property:

Scope(
  state: \.child,
  action: /Action.child,
  child: { childFeature } // childFeature is instantiated as a property of parent reducer. Thus, dependencies are propagated correctly
)

Instead of this:

Scope(
  state: \.child,
  action: /Action.child,
  child: { ChildFeature() } // childFeature is instantiated at the moment Reducer needs to reduce so it doesn't use propagated dependencies
)

I see this example extremely useful as it clearly shows which pitfalls need to be avoided if we want to get the most out of swift-dependencies right away. Without this example there is a vague which makes you think that probably TCA handles this somehow for you and dependencies will be propagated normally even if ChildReducer is initialised directly in body. Hence, some developers need to double check constructing some test projects and exploring how it actually works. All in all, I see that this one can potentially save someone's time and be a nice addition to the existing documentation.

Here is the link to the gist where the full example can be found: https://gist.github.com/evilhonda3030/2b2ced7ad8373df4e47a0b1b73f6b11d.js

Cheers and appreciate your hard work on making our tech stack better!

[stephencelis]

@evilhonda3030 Composable Architecture reducers and stores come with tools that integrate with swift-dependencies, so you should be using them instead of calling to withDependencies directly.

Instead of this:

let rootStore = Store(
    initialState: ParentFeature.State(value: 99, child: 99),
    reducer: { 
        withDependencies {
            $0.dummyDependency.value = { 10 }
        } operation: {
            ParentFeature()
        }
    }
)

Try this:

let rootStore = Store(
    initialState: ParentFeature.State(value: 99, child: 99)
) {
    ParentFeature()
} withDependencies: {
    $0.dummyDependency.value = { 10 }
}

[evilhonda3030]

Oh, great. Thanks a lot!

But this is an example when you want to override the dependencies for thy whole store. However, there are cases when you want to override dependencies for children reducers. What would be the most suitable API for that?

[stephencelis]

@evilhonda3030 There is Reducer.dependency and Reducer.transformDependencies.