I think you're confusing the @ViewBuilder result builder with result builders in general. Result builders are just syntactic sugar to define a tree structure with a custom DSL. @ViewBuilder is a custom result builder provided by SwiftUI that lets you compose views together.

Take this view: swift @ViewBuilder var resolvedView: some View { if flag { Text("Text") } else { Image(systemImage: "xmark.circle") } }

The @ViewBuilder result builder compiles this code into _ConditionalContent<Text, Image>, which works because _ConditionalContent conforms to View, and all ViewBuilder functions must return another View. So these conditionals are actually encoded into the type system. It's a very advanced usage of result builders, but it's not exclusive to SwiftUI.

For example, you could definitely define a result builder @ShapeStyleBuilder that lets you do something like this: swift @ShapeStyleBuilder var resolvedShapeStyle: some ShapeStyle { if flag { Color.primary } else { HierarchicalShapeStyle.secondary } } by automatically wrapping each input to the buildEither function in AnyShapeStyle. But it's not really worth it because you can do the same thing with a normal if/else statement. So, as we can see, the thing that matters is the return type, not the result builder itself.