I'm new to the swift evolution community, but I wanted to toss an idea out
there to get some feedback on it. So here it goes...
Currently, if you assign a non-nil value to an optional and then want to access
that optional later, in the same context, you need to manually unwrap the
value. This is usually done either by using "!" or by using something like "if
let" or guard.
What would it be like if the compiler could auto unwrap, in cases where in
knows the optional will have some value? This would make the code "clean" and
still be safe.
This concept of Auto Unwrapping of Optionals is similar to Implicitly Unwrapped
Optionals, but is only applied when the compiler knows it is safe to do so.
Take the following example:
class Test {
var today: NSDate? = nil
func test() {
today = today ?? NSDate()
print("Today is \(today)") // Would be printed as an optional
let timeInterval: NSTimeInterval = today!.timeIntervalSinceNow //
Requires ! or (if let) to unwrap
// ... do stuff with timeInterval ...
}
}
With the above example, the compiler could known that today has a value after
it's set in the test method. So why couldn't the compiler auto unwrap it when
accessed? This would mean manual unwrapping would be unnecessary:
class Test {
var today: NSDate? = nil
func test() {
today = today ?? NSDate()
print("Today is \(today)") // Would be printed as a value (not an
optional)
let timeInterval: NSTimeInterval = today.timeIntervalSinceNow // No !
required (auto unwrapped)
// ... do stuff with timeInterval ...
}
}
If the value later gets set to an optional value, then it will no longer be
auto unwrapable :
class Test {
var today: NSDate? = nil
func optionalDay() -> NSDate? {
return NSDate()
}
func test() {
today = today ?? NSDate()
print("Today is \(today)") // Would be printed as a value (not an
optional)
let timeInterval: NSTimeInterval = today.timeIntervalSinceNow // No
! required (auto unwrapped)
let timeInterval2: NSTimeInterval = today!.timeIntervalSinceNow //
Explicit unwrapping would still be allowed
// If today is assigned an optional value, we can no longer auto unwrap
it
today = optionalDay()
print("Today is \(today)") // Would be printed as an optional
let timeInterval3: NSTimeInterval = today!.timeIntervalSinceNow //
manual unwrapping would be required
}
}
Note in the above example, explicit unwrapping would still be allow. The
variable is still an optional. This allows for existing code to remain
unchanged.
This change would encourage less use of forced unwrapping "!", generally
require the developer to write less code, and would maintain code safety. On
the down side, it is performing some compiler “magic”. It would be yet another
thing to explain when trying to introduce people to swift and especially
optionals.
What do you all think, would something like this be worth pursuing, what other
pluses or minus would this introduce, has something like this already been
discussed?
Thanks,
Tod Cunningham
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