Non-state variable inside SwiftUI View

Question

I just rewatched Demistify SwiftUI and noticed that some of the examples use variable properties inside a SwiftUI View, without using the @State property wrapper. For example (around 19.04):

struct PurrDecibelView: View {
    var intensity: Double

    var body: some View {
        // ...
    }

It does not seem to be possible to change this property from any action defined in its body. Is there any reason for choosing a var over let here?

Answer 1

I can't see a reason for for choosing var over let in the specific case you have shared, but there could be some reasons like:

1. Default value and default initializer

If you set a default value to a let variable, it will not be present in the default initializer of the struct. But making it var will cause it to be an optional parameter:

2. Outside the body

Since View is just a protocol you conform to, there may be some reasons to have functionalities outside the body that you can control using mutating funcs:

struct PurrDecibelView {
    var intensity: Double

    mutating func increaseIntensity() {
        intensity += 1
    }
}

extension PurrDecibelView: View {
    var body: some View {
        Text("")
    }
}

3. Styleguide

Some teams and some companies prefer to always use var inside the structs and only control the mutability of the initiated objects.

_{💡 Not that I don't personally recommend or deny any of the above or any other reasons.}