Handling Multiple State Changes with onChange in TCA

[JongHyunLee84]

I have a question about the onChange method in Reducer.

I am currently transitioning my Combine-based project to TCA. Is there a way to handle multiple values at once in onChange, similar to how CombineLatest works in Combine?

For example, in Combine I have the following code:

Publishers.CombineLatest3($serviceAgree, $personalInfoAgree, $adAgree)
    .map { $0 && $1 && $2 }
    .assign(to: &$allAgree)

In TCA, I am currently using the following approach:

.onChange(of: \.serviceAgree) { _, _ in
    Reduce { state, _ in
        SyncAllAgree(&state)
    }
}
.onChange(of: \.personalInfoAgree) { _, _ in
    Reduce { state, _ in
        SyncAllAgree(&state)
    }
}
.onChange(of: \.adAgree) { _, _ in
    Reduce { state, _ in
        SyncAllAgree(&state)
    }
}

I also came across the following example code, but it was flagged as a deprecated:

.onChange(
  of: { ($0.userSettings.isHapticFeedbackEnabled, $0.userSettings.isPushEnabled) },
  removeDuplicates: ==
) { oldValue, newValue in
  Reduce { state, action in
    .run { send in
      // Persist new value...
    }
  }
}

Is there an alternative way to achieve this? If you have any solutions or suggestions, I would greatly appreciate it.

[mbrandonw]

Hi @JongHyunLee84, can you explain more what you mean by this:

but it was flagged as a duplicate

I believe that code should work just fine to be notified when any value in the tuple changes.

[JongHyunLee84]

@mbrandonw Sorry, I made a mistake when translating that the method was deprecated.

@available(*, deprecated, message: "Use 'onChange(of:)' with and equatable value, instead.")
  @inlinable
  public func onChange<V, R: Reducer>(
    of toValue: @escaping (State) -> V,
    removeDuplicates isDuplicate: @escaping (V, V) -> Bool,
    @ReducerBuilder<State, Action> _ reducer: @escaping (_ oldValue: V, _ newValue: V) -> R
  ) -> _OnChangeReducer<Self, V, R> {
    _OnChangeReducer(base: self, toValue: toValue, isDuplicate: isDuplicate, reducer: reducer)
  }