CODEWITHSUNDEEP
iosarraysswiftswift3
user3120670
user3120670

Reputation: 81

What is the difference between [[String:String]]! and [[String:String]]() in Swift

I am working on a project where I found an array variable

var items: [[String: String]]!

I searched in google how to define an empty array, I got the result as

var itemsNew: [[String: String]]()

while using items array getting an error while appending data

 self.appDelegate.items.append([Name: "sdsd",
                                 rate: "0.2",
                                 Quantity:"3",
                                 Taxable:"true",
                                  Category: "",
                                 inven: "true",
                                  amount : "0.23",
                                 mod: "",
                                 darray: "",
                                 list: "",
                                 famount: "0.0"])

giving an error "Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value: file". I am giving hardcore value but still, it's crashing. Don't know why it's crashing. can somebody help me?

Upvotes: 0

Views: 865

Answers (3)

Rupesh
Rupesh

Reputation: 141

[[String: String]]() is an object of Array of type [[String: String]].

Where as [[String: String]]! is an arrayType of type [[String: String]] which can't be nil while executing because it is an implicitly unwrapped optional.

You are getting Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value: file because items was never initialised. But you are trying to add an item to items which is actually a null value. You can solve this error by replacing items declaration with the below code.

var items: [[String: String]] = [[String: String]]()

And the declaration of itemsNew is also wrong. You can declare it as below.

var itemsNew = [[String: String]]()

or

var itemsNew: [[String: String]] = [[String: String]]()

Upvotes: 1

Frankenstein
Frankenstein

Reputation: 16341

The first object items is declared as an implicitly unwrapped optional. If you use it as items without the ? optionally unwrapping, you're saying that you know for sure that there is a value in items I'm sure it's not nil if it doesn't have a value I want the app to crash.

In the second case, you're creating a non-optional empty array of dictionary itemsNew which cannot be nil but is empty at the time of declaration. In summary, you can replace the optional declaration to empty declaration they would still store the same type in these properties.

var items = [[String: String]]()
var itemsNew = [[String: String]]()

Upvotes: 1

Ajjjjjjjj
Ajjjjjjjj

Reputation: 675

Because

var items: [[String: String]]! not allocating memory or giving back, the reference to item where developer can append the items.

So var itemsNew: [[String: String]]()is working as it is creating memory where you can append items.

Upvotes: 2

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