[swift-evolution] Prohibit invisible characters in identifier names

[David Sweeris]

> On Jun 24, 2016, at 08:27, Vladimir.S via swift-evolution <swift-evolution at swift.org> wrote:
> 
> (Personally I really don't understand why we need anything than ASCII codes for identifiers. This could solve all the problems with invisible space/left-to-right-flags/complicated rules/graphemes etc. But someone needs to be able to put dog emoji as identifiers.. well.. OK)

Math symbols make everything better (at least if you're into math).

- Dave Sweeris