[swift-evolution] NSString.contains(_:) returns false for empty string argument

Dave Abrahams dabrahams at apple.com
Sun Oct 2 13:59:10 CDT 2016

on Mon Sep 05 2016, Ole Begemann <swift-evolution at swift.org> wrote:

> Six weeks ago there was a discussion [1] (and a subsequent fix [2])
> about the behavior of `String.hasPrefix(_:)` and
> `String.hasSuffix(_:)` with empty string arguments. After the fix,
> `str.hasPrefix("")` always returns `true`.
> This leads to inconsistent behavior with the `NSString.contains(_:)`
> method, which returns `false` for an empty string argument:
>     let str = "Hello"
>     str.contains("") // returns false
> If `contains` were part of the stdlib like `hasPrefix` and `hasSuffix`
> are, I would consider this a bug. But `contains` comes from Foundation
> and I'm not sure how that changes things. Would it make sense to add a
> variant of `contains(_:)` to the stdlib and fix the behavior there?

It might be worth doing something for Swift 3.1

> I'm assuming it's too late for Swift 3 and it will be fixed with the
> String remodeling in Swift 4 anyway, 

That's my plan.

> but I just noticed this and I thought I'd ask.
> Ole
> [1]: https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160718/024630.html
> [2]: https://bugs.swift.org/browse/SR-2131
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