CODEWITHSUNDEEP
swift
pacification
pacification

Reputation: 6018

Why IndexSet can be initialized with negative one?

The documentation about IndexSet said:

The range of valid integer values is 0..<INT_MAX-1. Anything outside this range is an error.

But this code works fine:

let indexSet = IndexSet(integer: -1)

And if we try with -2, it will produce a crash as expected.

Why this happened? Is it a bug or i missed something?

Tested on Xcode 9.4.1, Swift 4.1.

Upvotes: 0

Views: 340

Answers (1)

ielyamani
ielyamani

Reputation: 18591

This is a bug. It comes from the fact that the initializer of an IndexSet is not failable. Here is the initializer as defined in the standard library:

/// Initialize an `IndexSet` with a single integer.
public init(integer: Element) {
    _handle = _MutablePairHandle(NSIndexSet(index: integer), copying: false)
}

Using unsigned integers should have been the way to go in order to be consistent with the definition:

The range of valid integer values is 0..<INT_MAX-1. Anything outside this range is an error.

You could have this extension to be safe:

extension IndexSet {
    public init(unsignedInt: UInt) {
        self = IndexSet(integer: Int(unsignedInt))
    }
}

So when you try to initialize an IndexSet with a negative integer, it will give you a proper error message:

IndexSet(unsignedInt: -1) //Negative integer '-1' overflows when stored into unsigned type 'UInt'

Upvotes: 2

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