null / nil in swift language

How would we define the following in swift programming language :

• null
• nil
• Nil
• [NSNull null]

In other words, what would be the swift equivalent of each of these objective c terms. Besides, would also like to know whether any specific use cases exist for non objective c types like structs and enums. Thanks in advance.

Regarding equivalents:

• NULL has no equivalent in Swift.
• nil is also called nil in Swift
• Nil has no equivalent in Swift
• [NSNull null] can be accessed in Swift as NSNull()

Note: These are my guesses based on reading and play. Corrections welcome.

But nil/NULL handling in Swift is very different from Objective C. It looks designed to enforce safety and care. Read up on optionals in the manual. Generally speaking a variable can't be NULL at all and when you need to represent the "absence of a value" you do so declaratively.

If you need to use a NULL at low level pointer operations, use the following:

UnsafePointer<Int8>.null()

nil means "no value" but is completely distinct in every other sense from Objective-C's nil.

It is assignable only to optional variables. It works with both literals and structs (i.e. it works with stack-based items, not just heap-based items).

Non-optional variables cannot be assigned nil even if they're classes (i.e. they live on the heap).

So it's explicitly not a NULL pointer and not similar to one. It shares the name because it is intended to be used for the same semantic reason.

Swift’s nil is not the same as nil in Objective-C.
In Objective-C, nil is a pointer to a non-existent object. In Swift, nil is not a pointer—it is the absence of a value of a certain type. Optionals of any type can be set to nil, not just object types.

• NULL has no equivalent in Swift.

• nil is also called nil in Swift

• Nil has no equivalent in Swift

• [NSNull null] can be accessed in Swift as NSNull()

The concept of Null in Swift resumes to the Optional enum. The enum is defined like this

enum Optional<T> {
  case Some(T)
  case None
}

What this means is that you cannot have an uninitialised variable/constant in Swift.. If you try to do this, you will get a compiler error saying that the variable/constant cannot be uninitialised. You will need to wrap it in the Optional enum..

This is the only Null concept you will find in Swift