See also: Defunctionalization.

You can think of a SwiftUI view as a defunctionalized function. The parameters to the function are the properties of the struct. The body is the return type of the function. We cannot call the function ourselves: instead, the framework can call it. It passes in things like the environment, the attribute graph handlers (e.g. to create new nodes, etc). The body contains the return type of the function call.

SwiftUI views are defunctionalized so that they can be compared for equality and prevent unnecessary view updates.