CODEWITHSUNDEEP
arraysswift
matt
matt

Reputation: 535989

Bug in Swift's notion of Array equality?

Try this:

    let url1 = NSURL(string: "foo bar")
    let url2 = NSURL(string: "http://www.apple.com")
    var arr1 = NSURL[]()
    var arr2 = NSURL[]()
    // one order
    arr1 += url1
    arr1 += url2
    // other order
    arr2 += url2
    arr2 += url1
    // equality test
    println(arr1 == arr2) // true!?

After some experimentation, I think this has to do with Optionals. url1 comes back as nil, so to form an array of both urls, Swift has to treat these arrays (I'm guessing) as arrays of Optional<NSURL>. But I still think it's a bug; it's as if the notion of comparing an array of optional NSURLs causes Swift to throw up its hands somehow... And, one might argue, it's a bug in another sense too, because I explicitly typed these arrays as NSURL[]; I didn't say NSURL?[], so why is Swift permitting an Optional to go into them in the first place?

I'm wondering if anyone has noticed anything similar that might throw light on the matter. (I don't think this post is related, though of course I could be wrong.)

EDIT Some people have expressed an inability to reproduce the issue, so I've posted an example project at https://github.com/mattneub/SwiftArrayEqualityTest

Upvotes: 1

Views: 686

Answers (1)

Nate Cook
Nate Cook

Reputation: 93296

In fact, all instances from the Objective-C APIs (essentially any UI* or NS* class) are actually optional, despite not appearing to be so via declaration, since Objective-C types can always be nil. An array of NSURL is essentially an array of implicitly unwrapped optional NSURLs, or NSURL![].

(I explained more in this answer.)

So it isn't a bug that the array can take a nil value, but it is a bug that the two evaluate to equal. Get thee to bugreport.apple.com.

Upvotes: 3

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