[swift-evolution] [Review] Tuple comparison operators (was: Add a Lazy flatMap for Sequences of Optionals)

Guillaume Lessard glessard at tffenterprises.com
Tue Dec 22 12:39:43 CST 2015

I wholeheartedly support the Equatable (==) portion of this proposal.
I’m quite negative about the Comparable portion; it doesn’t really make sense.

The justification for making Tuples comparable pretty much consists of hand-waving.
Why should (0,3,4) be smaller than (0,5,0)? Beats me.
Why would it be the other way around? Also beats me.

I can vaguely see the utility of Comparable when I squint, but the actual behaviour would require extensive documentation with caveats about it not really making any sense. To overload an operator with a clear meaning with a behaviour with a wishy-washy definition is a bad idea.

* Is the problem being addressed significant enough to warrant a change to Swift?

Yes for Equatable.
No for Comparable.

* Does this proposal fit well with the feel and direction of Swift?

Yes for Equatable.
No for Comparable.

* If you have you used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?

I have used Mathematics during an extensive education in Physics and Engineering, at the end of which I escaped with a Ph.D. from a major institution.

Making arbitrary Tuples Equatable when possible makes sense.
Making them Comparable absolutely does not.

Comparability is domain-specific. The standard library cannot know what an arbitrary Tuple means.

* How much effort did you put into your review? A glance, a quick reading, or an in-depth study?

I drew upon my experience. While I feel it’s on solid footing, I would hesitate to call it an in-depth study.

Finally, I would like to note that I would support a free-standing function with a clear name that does the same thing as the proposed overloads of the comparison operator.

Guillaume Lessard

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