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Swift NSSet & CoreData


for aresponse in
self.response.question.responses {
    // this next line throws an error
    var scoreVal = aresponse.score.integerValue

The problem is that for aresponse in ... responses is iterating through an NSSet. Swift doesn't know what is in the NSSet, so it treats each value aresponse as an AnyObject, which has no properties. Thus, the compiler complains when you try to get the score property of aresponse.

You, on the other hand, know that each value aresponse is a Response. So you need to tell Swift this, by casting (with as). Note that you were in fact doing that in your Objective-C code:

for(Response *aresponse in
self.response.question.responses)

But you have forgotten to do the same thing in Swift. You can do it in various ways; for example you could write this sort of thing:

for aresponse in
self.response.question.responses {
    var scoreVal = (aresponse as
Response).score.integerValue

That gets us past the compiler, which now shares in our knowledge of what this variable really is.

Once you get used to this, you will be kissing the ground that Swift walks on. All this time, in Objective-C, you were making assumptions about what kind of object you had, but in fact what you had was an id and the compiler was letting you send any message at all to it - and so, you would often crash with "unrecognized selector". In Swift, an "unrecognized selector" crash is basically impossible because the type of everything is specified and the compiler won't let you send an inappropriate message to an object in the first place.


Categories : IOS

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