CODEWITHSUNDEEP
swiftxcodegenericscompiler-errorssegmentation-fault
gannonbarnett
gannonbarnett

Reputation: 1965

Xcode 8.2 Swift Compiler Error: "Segmentation Fault: 11"

This function works correctly when I don't implement it generically (just with ints), but when I go to make it generic, changing only a few letters with no obvious errors, Swift is unable to compile it; I don't even use the func, simply having the file in my project crashes it.

Xcode says that "an internal error has occurred." I checked the stack trace, and the error is listed as "Segmentation Fault: 11." I'll post my code below.

I can also post the stack trace upon request.

import Foundation

func BinSearch<T : Comparable>(elements: [T], target: T) -> Int?{
    let maxIndex = elements.count - 1
    var rightIndex = maxIndex
    var leftIndex = 0
    var middleIndex : Int {return lround(Double((rightIndex + leftIndex)) / 2)}

    var maxVal : T {return elements[rightIndex]}
    var middleVal : T {return elements[middleIndex]}
    var minVal : T {return elements[leftIndex]}

    while elements[middleIndex] != target {
        //test if in infinite loop for target within range of array but DNE
        if leftIndex == middleIndex || rightIndex == middleIndex && rightIndex != 1{
            return nil
        }

        //prevent infinite loop due to rounding method
        if rightIndex == 1 {
            return leftIndex
        }

        //core code
        if target > middleVal {
            leftIndex = middleIndex
        }else {
            rightIndex = middleIndex
        }
    }
    return middleIndex
}

Upvotes: 4

Views: 3238

Answers (2)

Alexis C.
Alexis C.

Reputation: 4918

In my case I got this error when using typealias in old Swift 2 format in a Swift 3 environment, for instance :

(Void -> Void) instead of (() -> ())

Upvotes: 1

Martin R
Martin R

Reputation: 539745

The compiler should not crash, no matter how "wrong" the source code is, so you might consider to file a bug report.

In this case, the problem seems to be that middleVal is a computed property. If you replace

    //core code
    if target > middleVal {
        leftIndex = middleIndex
    }else {
        rightIndex = middleIndex
    }

by

    //core code
    if target > elements[middleIndex] {
        leftIndex = middleIndex
    }else {
        rightIndex = middleIndex
    }

then the code compiles. However, it does not work correctly. For example

 BinSearch(elements: [3, 4, 5], target: 2)

returns 0 instead of nil. (Also I see no advantage in using computed properties for middleIndex and middleVal. maxVal and minVal are not used at all in your code.)

Here is an example of a correctly working implementation (inspired by http://rosettacode.org/wiki/Binary_search#Swift):

func binarySearch<T : Comparable>(elements: [T], target: T) -> Int? {
    var leftIndex = 0
    var rightIndex = elements.count - 1

    while leftIndex <= rightIndex {
        let middleIndex = (leftIndex + rightIndex) / 2
        if elements[middleIndex] < target {
            leftIndex = middleIndex + 1 // Continue search in upper half.
        } else if target < elements[middleIndex] {
            rightIndex = middleIndex - 1 // Continue search in lower half.
        } else {
            return middleIndex // Found.
        }
    }
    return nil // Not found.
}

Upvotes: 1

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