[swift-evolution] Synthesizing Equatable, Hashable, and Comparable for tuple types

[Xiaodi Wu]

On Thu, Nov 23, 2017 at 16:45 Kelvin Ma via swift-evolution <
swift-evolution at swift.org> wrote:

>
>
> On Thu, Nov 23, 2017 at 12:32 PM, Tino Heth <2th at gmx.de> wrote:
>
>>
>> a good idea on paper, a disastrous one in practice. What happens if every
>> geometry library declares their own Point type?
>>
>> That would be ugly („disastrous“ imho is a little bit to strong — C++
>> had/has similar issues, and other languages as well)
>> But if there would be a simple Point struct in a library that is popular
>> (could be achieved by shipping it alongside the stdlib), this problem would
>> be solved (there has been a pitch lately, but I guess it faded away
>> silently).
>>
>
> it’s ugly in C++ and disastrous in Swift because C++ has fixed layout
> guarantees and everyone agrees that z comes after y comes after x, so you
> can unsafe-bitcast the foreign C++ points into your own points “for free”.
> you can’t do the same thing in Swift
>

Why do you need to have this ability to unsafe bitcast? Is interconversion
between point types such a common operation that it's a performance
bottleneck?
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