is swift built on top of objective c
Swift uses the same runtime as the extant Objective-C system, but requires iOS 7 or macOS 10.9 or higher. Swift and Objective-C code can be used in one program, and by extension, C and C++ also. In contrast to C, C++ code cannot be used directly from Swift. An Objective-C or C wrapper must be created between Swift and C++. In the case of Objective-C, Swift has considerable access to the object model, and can be used to subclass, extend and use Objective-C code to provide protocol support. The converse is not true: a Swift class cannot be subclassed in Objective-C.
Swift (programming language)