[swift-evolution] [review] SE-0096: Converting dynamicType from a property to an operator

David Ungar ungar at icloud.com
Tue May 24 17:11:20 CDT 2016


I love the desire for consistency in this proposal, but it brings up two issues:

1. Swift’s take on standalone functions vs member functions: As Swift has progressed, it seems to have adopted a preference (which I like) in favor of members over functions that just take arguments. I think that having “dynamicType” as a property is more consistent with this direction. I like the direction because the flow of the computation is from left-to-right. (I also have adopted the pipe operator “|>” in my programming style for the same reason.) I love this aspect of a more functional style. In fact, I would rather move “sizeof” to be a property, maybe call it “bytesize”.

2. Stratification: But there’s a deeper issue. What direction should Swift be taking for reflection? For example, there might be a useful subset of Swift for very performance-critical applications in which there is no dynamic type information. In that case, would it make sense to put “dynamicType” in a separate box? If so, the syntax could be something like “Mirror(reflecting: <someExpression>).dynamicType” where this dynamicType returned a “mirror” on the type information. I’m not advocating this alternative, but this direction has significant both pros and cons. If this is something that the Swift team wants to consider in the future, it might be better to leave “dynamicType” alone for now. (For more info, see http://bracha.org/mirrors.pdf and http://bracha.org/mirrors-oopsla04.pdf.)

Thank you,

- David Ungar

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