[swift-evolution] Feature proposal: Range operator with step
dabrahams at apple.com
Wed Apr 6 16:03:15 CDT 2016
on Wed Apr 06 2016, Erica Sadun <swift-evolution at swift.org> wrote:
> On Apr 6, 2016, at 2:17 PM, Dave Abrahams via swift-evolution
> <swift-evolution at swift.org> wrote:
> When using odd integer literals to produce an even number sequence,
> prefer the `...` operator to the `..<` operator and change your ending
> literal to an even number.
> I don't think you can fix counterintuitive behavior with guidance.
> (1..<199).striding(by: -2) is the first way I'd reach for to express
> 197, 195, ..., 3, 1
> Yes, but you can with warnings and fixits.
> * The compiler should issue a warning for any use of
> (n..<m).striding(by: v | v < 0) | n, m, v : Integer
> with a fixit of "replace (n..<m) with (n...m - 1)" regardless of
> whether n or m is known at compile time
> * If v cannot be known at compile time, I think the compiler should
> always prefer ... to ..<.
> * The compiler should not allow
> (n..<m).striding(by: v | v < 0) | n, m, v: floating point types
> where v is known at compile time to be a negative constant. There should
> also be a runtime precondition that raises a fatal error should a negative
> v be used with a half-open interval.
You can lessen the impact of any design choice by adding warnings and
fixits, but I'm pretty sure it's better to make a choice that doesn't
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