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up vote 0 down vote favorite

I am burdened with the requirement of interacting with a C based library, which has a bunch of constant sized arrays (e.g. char[17]).

When trying to assign or read those properties from swift, they are represented as a Tuple type of that size..

As far as I know, you can't access tuples with subscripts, and it is not trivial to convert an array to a tuple .. so I am left with this ugly code to interact with the library:

Note for the curious: The C library uses the eatLength to determine which values of the tuple are valid, and which shouldn't be considered. That is why I don't care about what the padded value is.

typedef struct _DMMove
{
    uint8_t steps[17];
    uint8_t eats[16];
    uint8_t eatLength;
} DMMove;

extension DMMove {

    init(steps: [Int], eats: [Int]) {

        var paddedSteps = Array(0..<17) as [UInt8]
        var paddedEats = Array(0..<16) as [UInt8]

        for (i, v) in enumerate(steps) {
            paddedSteps[i] = Int8(v)
        }

        for (i, v) in enumerate(eats) {
            paddedEats[i] = Int8(v)
        }

        var stepsTuple = (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0) as (Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8)
        var eatsTuple = (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0) as (Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8,Int8)

        stepsTuple.0 = paddedSteps[0]
        stepsTuple.1 = paddedSteps[1]
        stepsTuple.2 = paddedSteps[2]
        stepsTuple.3 = paddedSteps[3]
        stepsTuple.4 = paddedSteps[4]
        stepsTuple.5 = paddedSteps[5]
        stepsTuple.6 = paddedSteps[6]
        stepsTuple.7 = paddedSteps[7]
        stepsTuple.8 = paddedSteps[8]
        stepsTuple.9 = paddedSteps[9]
        stepsTuple.10 = paddedSteps[10]
        stepsTuple.11 = paddedSteps[11]
        stepsTuple.12 = paddedSteps[12]
        stepsTuple.13 = paddedSteps[13]
        stepsTuple.14 = paddedSteps[14]
        stepsTuple.15 = paddedSteps[15]
        stepsTuple.16 = paddedSteps[16]

        eatsTuple.0 = paddedEats[0]
        eatsTuple.1 = paddedEats[1]
        eatsTuple.2 = paddedEats[2]
        eatsTuple.3 = paddedEats[3]
        eatsTuple.4 = paddedEats[4]
        eatsTuple.5 = paddedEats[5]
        eatsTuple.6 = paddedEats[6]
        eatsTuple.7 = paddedEats[7]
        eatsTuple.8 = paddedEats[8]
        eatsTuple.9 = paddedEats[9]
        eatsTuple.10 = paddedEats[10]
        eatsTuple.11 = paddedEats[11]
        eatsTuple.12 = paddedEats[12]
        eatsTuple.13 = paddedEats[13]
        eatsTuple.14 = paddedEats[14]
        eatsTuple.15 = paddedEats[15]

        self.init(
            steps: stepsTuple,
            eats: eatsTuple,
            eatLength: Int16(eats.count)
        )
    }

}

More Notes

If you don't know how a C struct is exposed to Swift, well it's as simple as though there is an actual Swift struct with an init that takes all the struct's attributes as parameters.

I am sure someone will suggest using Tuple initializers ... Here ya go:

Swift compiler fail

Expression was too complex to be solved in reasonable time; consider breaking up the expression into distinct sub-expressions

share|improve this question
    
Is that exception from Playground? Have you tried the same thing in a non-Playground? –  nhgrif Mar 19 at 20:46
    
@nhgrif It isn't from playground, this is the actual code base that I need to optimize –  Mazyod Mar 19 at 20:50
    
Okay, so for clarification... you've got an array of values you built in Swift, and you need to pass an array to a C-library? –  nhgrif Mar 19 at 20:58
    
Can you include the thing you're extending in the question (or at least a link to it)? –  nhgrif Mar 19 at 21:22
    
@nhgrif I already added it, thought it was obvious –  Mazyod Mar 19 at 21:23

2 Answers 2

up vote 0 down vote accepted

Hmm.. Quite simpler than expected. Mind you, it obviously won't work for collection types because of the underlying memory representation.

extension DMMove {

    typealias StepsType = (UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8)
    typealias EatsType = (UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8,UInt8)

    init(steps: [Int], eats: [Int]) {

        var paddedSteps = steps.map { UInt8(GUIIndex: $0) }
        var paddedEats = eats.map { UInt8(GUIIndex: $0) }

        paddedSteps.extend(Array(UInt8(steps.count)..<17))
        paddedEats.extend(Array(UInt8(eats.count)..<16))

        var stepsTuple = UnsafeMutablePointer<StepsType>(malloc(UInt(sizeof(StepsType))))
        var eatsTuple = UnsafeMutablePointer<EatsType>(malloc(UInt(sizeof(EatsType))))

        memcpy(stepsTuple, paddedSteps, UInt(paddedSteps.count))
        memcpy(eatsTuple, paddedEats, UInt(paddedEats.count))

        self.init(
            steps: stepsTuple.memory,
            eats: eatsTuple.memory,
            eatLength: UInt8(eats.count)
        )
    }
}
share|improve this answer
up vote -1 down vote

I found this reflection based solution on Stack Overflow, and I tailored it a bit into the following:

func arrayForTuple<T,E>(tuple:T) -> [E] {
    let reflection = reflect(tuple)
    var arr : [E] = []
    for i in 0..<reflection.count {
        if let value = reflection[i].1.value as? E {
            arr.append(value)
        }
    }
    return arr
}

let name : (Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8, Int8) = (65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74)
let nameArray : [Int8] = arrayForTuple(name)

It works almost like map() except it's not guaranteed to return a 1:1 array. E.g. if the tuple contains an element which is not an Int8, it will be skipped.

share|improve this answer
    
Thanks, this will be useful in the future, but per the title, the question is to convert an array to a tuple, not the other way around –  Mazyod Mar 20 at 14:08

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