func withUnsafeBytes<T, Result>(of: inout T, _: (UnsafeRawBufferPointer) throws -> Result) Invokes body with an UnsafeRawBufferPointer argument and returns the result. Declaration func withUnsafeBytes<T, Result>(of arg: inout T, _ body: (UnsafeRawBufferPointer) throws -> Result) rethrows -> Result