TIL SwiftUI View's Instance Method `onChange(of:initial:_:)`

Have found strange declaration in SwiftUI sources as for me:

@available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
public typealias ObservableObject = ObservableObject

TIL SwiftUI View’s Instance Method onChange(of:initial:_:)