array_internal_storage.swift

extension Array {
    func sharesStorageWith(other: Array<T>) -> Bool {
        let thisPtr: UnsafePointer<T> = self.withUnsafePointerToElements { return $0 }
        let otherPtr: UnsafePointer<T> = other.withUnsafePointerToElements { return $0 }
        return (thisPtr == otherPtr)
    }
}

var a1: Array<Int> = [10, 11]
a1.append(20)
println(a1.sharesStorageWith(a1)) // true

var a2 = a1
var a3 = a1
// Now all of a1, a2 and a3 use the same
// underlying buffer.
println(a1.sharesStorageWith(a2)) // true
println(a2.sharesStorageWith(a3)) // true

a1.append(30)
// Now a1 uses a different buffer.
// a2 and a3 are still sharing data.
println(a1.sharesStorageWith(a2)) // false
println(a2.sharesStorageWith(a3)) // true

a3.unshare()
// a2 and a3 are no longer sharing data.
println(a2.sharesStorageWith(a3)) // false

var a4 = a1.copy()
// The copy() makes a4 not share a1's data
println(a1.sharesStorageWith(a4)) // false