How to test for undefined array?

Question

I am using this line of code

let transactions = SKPaymentQueue.default().transactions

This is what Apple amazing docs has to say about transactions.

What is exactly "undefined"? How do I test transactions before proceeding in code?

I have an observed attached to the payment queue.

I can guarantee you that undefined is not nil, because I have tested for nil and Xcode whined with an error

Comparing non-optional value of type '[SKPaymentTransaction]' to 'nil' always returns false

is undefined the new "empty array"? If not, how do I test for that?

Print it out in the debugger and see what you get? That's usually what I do. Or print() it. — dandan78
– dandan78, Commented Aug 26, 2019 at 15:04
The type is [SKPaymentTransaction] (a.k.a. Array<SKPaymentAction>], not [SKPaymentTransaction]?. So out of all of the possible actions the framework can take, returning nil isn't possible. — Alexander
– Alexander, Commented Aug 26, 2019 at 16:14
How do you test something that is “undefined”? You don’t. The documentation is explicitly advising that this property is not defined (i.e. not reliable/usable) until some observers are attached to the queue. — Rob
– Rob, Commented Aug 26, 2019 at 21:06

Alexander · Accepted Answer · 2019-08-26 16:12:48Z

3

Undefined means literally that: the API does not define what the framework will do. Anything is "fair game".

The code might cause a fatal error, return an empty array, or trigger a workflow to send a postcard to you in the mail. It's not defined.

However, no matter what the current behaviour happens to be, you shouldn't depend on it. It might return an empty array today, but crash tomorrow. Because the API explicitly documents the behaviour as undefined, Apple is free to change implementation details, without them counting as "API breaking changes".

answered Aug 26, 2019 at 16:12

Alexander

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