Swift array set value of index not working

Question

I have a method (contents below) where queue2 is just an [Int]. I printed a lot of things to see if everything was working up to a point.

public func cool(item: Int) {
    println(item)
    println(back)
    //queue2.insert(item, atIndex: back)
    queue2[back] = item
    println(queue2.description)
    println("done")
}

The problem is this fails at runtime and I don't know why. Apple docs say you can set the value of any index in an array with this notation, but it doesn't work. If I uncomment the commented line and comment out the one below it, everything runs fine but it doesn't provide the functionality I need. What gives?

It stops execution with a exc_bad_instruction (code=exc_i386_invop subcode=0x0) — Sheen D
– Sheen D, Commented Jul 21, 2015 at 1:40
back = 0, and the queue is initiated to an array with capacity 20. — Sheen D
– Sheen D, Commented Jul 21, 2015 at 1:42

matt · Accepted Answer · 2015-07-21 01:45:43Z

2

If queue2 is empty, this line is illegal no matter what back is:

queue2[back] = item

You cannot refer to an index that doesn't exist, and an empty array has no indexes (indices).

answered Jul 21, 2015 at 1:45

matt

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2 Comments

matt Over a year ago

As for what happens when you use queue2.insert(item, atIndex: back), the problem here is that you say "it doesn't provide the functionality I need", but you have not explained what that functionality is. That code is doing exactly what you are asking it to do; neither it, nor we, have any way of knowing what else you might have had in mind...

iOS Developer Over a year ago

how can i do that if i want? as its not posssible but i want to do that? can i realy do that?

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