[swift-evolution] Improvement proposal: change overflow behavior in successor()/predecessor() methods for Int types

[Dmitri Gribenko]

On Thu, Apr 7, 2016 at 12:20 AM, Vladimir.S via swift-evolution
<swift-evolution at swift.org> wrote:
> But. .successor() .predecessor() methods for Int values do not follow these
> rules for overflow situations. I.e. :
> let i : Int8 = Int8.max
> let k : Int8 = i.successor()
> - is OK for current Swift compiler. We have i==127 and k==-128, no run-time
> error.

This was done for performance reasons.  Array's indices are Ints, and
adding an overflow check here was causing significant performance
issues when iterating over arrays.  These methods were not designed to
be used in contexts other than indices.  When ints are used as
indices, doing an overflow check in successor() does not prevent any
mistakes, since Array's bounds are always tighter than
Int.min...Int.max.

These methods are going away in the new indexing model.
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160229/011552.html

Dmitri

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