Argument type 'Int' does not conform to expected type 'NSCoding & NSCopying & NSObjectProtocol'

Question

I am new to Swift and was trying some tutorials to learn and polish my knowledge on Swift. I stumbled upon above error in this code which I didn't understand. In case anyone of you have idea, please explain whats wrong here.

    let textChoices =   [
    ORKTextChoice(text: "Create a ResearchKit app", value:0),
    ORKTextChoice(text: "Seek the Holy grail", value:1),
    ORKTextChoice(text: "Find a shrubbery", value:2)
]

I resolved the error by suggestion provided by Xcode and now my code looks like

    let textChoices =   [
    ORKTextChoice(text: "Create a ResearchKit app", value:0 as NSCoding & NSCopying & NSObjectProtocol),
    ORKTextChoice(text: "Seek the Holy grail", value:1 as NSCoding & NSCopying & NSObjectProtocol),
    ORKTextChoice(text: "Find a shrubbery", value:2 as NSCoding & NSCopying & NSObjectProtocol)
]

There is another solution I got from answer. While it works, I am still not clear about the problem and solution. What is the concept I am missing.

Hamish · Accepted Answer · 2016-10-08T19:08:14.517

As ORKTextChoice's initialiser has an abstract parameter type for value:, Swift will fallback on interpreting the integer literals passed to it as Int – which does not conform to NSCoding, NSCopying or NSObjectProtocol. It's Objective-C counterpart, NSNumber, however does.

Although, rather than casting to NSCoding & NSCopying & NSObjectProtocol, which would result in a bridge to NSNumber (albeit an indirect and unclear one), you can simply make this bridge directly:

let textChoices = [
    ORKTextChoice(text: "Create a ResearchKit app", value: 0 as NSNumber),
    ORKTextChoice(text: "Seek the Holy grail", value: 1 as NSNumber),
    ORKTextChoice(text: "Find a shrubbery", value: 2 as NSNumber)
]

Your original code would have worked prior to Swift 3, as Swift types were able to be implicitly bridged to their Objective-C counterparts. However, as per SE-0072: Fully eliminate implicit bridging conversions from Swift, this is no longer the case. You need to make the bridge explicit with as.

Argument type 'Int' does not conform to expected type 'NSCoding & NSCopying & NSObjectProtocol'

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