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Confused with underscore in init, assigning a default value, and .onAppear

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In the CoreDataProject project and in the BucketList project, Paul has us using the underscore in a View's initializer to assign some value to a State, StateObject, or FetchRequest. I'm somewhat confused why we're doing this.

I've tried making some more basic code to see what's going on. It's seems assigning a default value by doing: @State private var text = "Hello world!", using .onAppear: .onAppear { text = "Hello, galaxy!"}, or using the struct's initializer achieve the same thing and set a value for the text property when the view is loaded. Up to this point, I've mostly used .onAppear to set things when the screen loads but maybe the initializer is a better place to set these things. Can someone please explain what the benefit is of using one approach over another?

struct ContentView: View {
    @State private var text = "Hello world!"

    var body: some View {
        NavigationView {
            Form {
            .onAppear { text = "Hello, galaxy!"}
    init() {
        _text = State(initialValue: "Hello, solar system!")


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