[swift-evolution] Default Generic Arguments

Alexis abeingessner at apple.com
Thu Jan 26 18:14:53 CST 2017

> On Jan 26, 2017, at 4:26 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> Very interesting point, Alexis. So can you reiterate again which of the four options you outlined earlier support this use case? And if there are multiple, which would be the most consistent with the rest of the language?

Both “prefer user” and “DWIM” are consistent with my desired solution for this specific problem (they pick Int64). DWIM seems more consistent with the rest of Swift to me in that it tries harder to find a reasonable interpretation of your code before giving up. I think it also ends up having the simplest implementation in the current compiler. You can potentially just add a new tie-breaker if-statement in this code: https://github.com/apple/swift/blob/master/lib/Sema/CSRanking.cpp#L1010 <https://github.com/apple/swift/blob/master/lib/Sema/CSRanking.cpp#L1010>

Something to the affect of “if one of these was recommended by a generic default, that one’s better”. This of course requires threading that information through the compiler.

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