Why is an optional array not enumerable in Swift? What's the best way to make it work?
e.g.
var objs:String[]?
// Won't work
for obj in objs {
}
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2 Answers
You first need to "unwrap" the optional, or in other words, validate if it is nil or not:
if let actualObjs = objs {
for obj in actualObjs {
}
}
actualObjs becomes type: String[] and the block is run with it if objs is not nil. If objs is nil, the block will just be skipped. (For more information on this, read Apple's Documentation)
If you are positive that objs is not nil, you can also just use the force unwrap operator (!):
for obj in objs! {
}
If objs is nil in this case, it will throw a runtime error and the whole program will stop.
Note: The practical reason you need to unwrap the optional, is that an Optional is its own type in Swift:
enum Optional<T>
So when you try to interact with the Optional directly, you are really interacting with an enum. That enum just happens to store the real value within it. (hence the name "unwrap")
4 Comments
manojlds
What's
let actualObjs = objs doing? Can you explain?
drewag
@manojlds "if let" is a special syntax for unwrapping optionals (and some other things). There isn't much to be said other than it tests if the optional is nil. If it is not nil, it assigns the value to "actualObjs" as a normal (non-optional) value and runs the
if blockmanojlds
@drewag - ah, ok thanks. Is there a documentation link explaining this? Wasn't able to find it.
=====Swift 2.1=====
objs?.forEach {
print($0) // $0 is obj
}
the same as
objs?.forEach { obj in
// Do something with `obj`
}
=====Swift 1.2=====
If you want to enumerate objs that is still be [String]?,
Try it
for i in 0 ..< (objs?.count ?? 0) {
let obj = objs?[i]
}
