example Swift 3 withMemoryRebound

gistfile1.txt

so A and B are structurally identical
C reverses the order of the 8 and 32 bit Ints
and D substitutes a string for the Int8
then I try to read aaaa’s bits using B C and D overlays 😊
C is printing the 8 bits of the A integer j and then the first 8 bits of integer k but somehow that still works out to one

when I hit D it doesn’t find a string so prints a blank

but the important point is: it doesn’t check anything, and doesn’t crash

so ‘undefined behavior’, as it should be

func newInSwift3 () {
  

        class A {
            var j: Int8 = 1
            var k: Int32 = 3
        }

        class B {
            var j: Int8 = 2
            var k: Int32 = 4
        }

        class C {
            var j: Int32 = 5
            var k: Int8 = 7
        }

        class D {
            var j: String = "hello"
            var k: Int32 = 9

        }

        var aa = A()
        let bb = B()
        let cc = C()
        let dd = D()


        var unsfmut : UnsafeMutablePointer<A> = UnsafeMutablePointer<A>.allocate(capacity: 1)
        unsfmut.initialize(to: aa)

        let aaa = UnsafePointer<A>(unsfmut)

        var aaaa : A = A()
        aaaa = unsfmut.pointee
        aaaa = aaa.pointee
        print ("j is \(aaaa.j)")


        withUnsafePointer(to: &aa) { (ptr: UnsafePointer<A>) in
            let vptr = UnsafeRawPointer(ptr)
            ptr.withMemoryRebound(to: B.self, capacity: 1) {

                var z1 = $0 as UnsafeMutablePointer<B>

                var bbbb : B = B()
                bbbb = z1.pointee
                print ("bbbb.j \(bbbb.j)")

            }
            ptr.withMemoryRebound(to: C.self, capacity: 1) {

                var z2 = $0 as UnsafeMutablePointer<C>

                var cccc : C = C()
                cccc = z2.pointee
                print ("cccc.j \(cccc.j)")

            }
            ptr.withMemoryRebound(to: D.self, capacity: 1) {

                var z3 = $0 as UnsafeMutablePointer<D>

                var dddd : D = D()
                dddd = z3.pointee
                print ("dddd.j \(dddd.j)")

            }
        }


    }