SwiftUI View extension restrict where clause lead to crash

Question

I try to write View extension by restrict where clause,code is very simple:

struct FooView : View {
 var body: some View {
 VStack {
 Text("hello world")
 }
 }
}
// only FooView type can invoke standard()
extension View where Self == FooView {
 func standard() -> some View {
 self
 .frame(width: 200, height: 50)
 }
}

I call standard() like this:

struct ContentView: View {
 
 var body: some View {
 
 VStack {
 FooView()
 .standard()
 }
 }
}

But run it will crashed in Xcode Preview! (Xcode 12.2 + MacOS 10.15.7) Is there something wrong with what I wrote? Thanks ;)

• David Pasztor: Why don't you just extend FooView instead of View?
• hopy: @DávidPásztor you're right!but I just want to know extend from View why not working. ;)
• Adam: @hopy any luck with this? am curious to find out as well. I wonder if its because is not a protocol. as the error says something about protocol witness etc..
• hopy: @Adam I'm not sure... Maybe I should try it in the latest Xcode 14 ;)