ios – Might I do know why some model of code will trigger “Sort ‘()’ can not conform to ‘View'” in Swift UI?

I used to be questioning, why some model of code will trigger “Sort ‘()’ can not conform to ‘View'” in Swift UI?

The next code is OK

struct ContentView: View {
    var physique: some View {
        var a = 100
        
        VStack {
            Textual content("Hiya, world!")
        }
        .padding()
    }
}

The next code causes error

struct ContentView: View {
    var physique: some View {
        var a = 100
        a = 999
        
        VStack {
            Textual content("Hiya, world!")
        }
        .padding()
    }
}

The code will trigger

Sort '()' can not conform to 'View

Might I do know why it’s so? Is that this restriction imposed by Swift language, or imposed by SwiftUI framework?

My information is in UIKit, and I’m new to SwiftUI.

Thanks.