[swift-evolution] [swift-evolution-announce] [Review] SE-0041: Updating Protocol Naming Conventions for Conversions

Chris Lattner clattner at apple.com
Tue May 10 19:51:37 CDT 2016

> On May 10, 2016, at 11:48 AM, Chris Lattner <clattner at apple.com> wrote:
> Hello Swift community,
> The review of "SE-0041: Updating Protocol Naming Conventions for Conversions" begins now and runs through May 16. The proposal is available here:
> 	https://github.com/apple/swift-evolution/blob/master/proposals/0041-conversion-protocol-conventions.md

Here are comments from someone who preferred to stay anonymous.  These are not my own:

* What is your evaluation of the proposal?

I rather agree with the comments mentioned in the proposal from the Standard Library design team, in that I agree with the basic intention of the proposal, but I’m not convinced about the proposed answer. Specifically:

1) I agree with the proposal that Representable seems more suited to meaning “a representation can be created from this type”. This is in line with existing Cocoa APIs that use “dictionaryRepresentation” to generate a dictionary that represents the object (for e.g. serialization to JSON). See, for example, NSUbiquitousKeyValueStore, NSUserDefaults, and SCNTechnique. Out of those, only the last one can also be initialized from a dictionary, so the term “representation” as used in existing Cocoa frameworks seems better suited for implying only a one-way conversion (and also feels natural to me).

2) I’m not convinced on Creatable. I’ve been using Convertible for protocols that imply that the type can be initialized from another type (e.g. the DictionaryConvertible protocol would contain init(dictionary:), and thus SCNTechnique would conform to it). This also seems in line with the bulk of the “Convertible” protocols in the standard library today. The word “creatable" strikes me as strange, because the term “create” isn’t used anywhere else in regards to initialization that I know of.

3) I’m not positive that we need a third protocol that implies bidirectionality. I’m not opposed to it, but if raw values conformed to both RawConvertible and RawRepresentable to indicate both their initialization and generated representation qualities, I’d be fine with that. And then maybe there’s just a typealias for RawValueProtocol that combines those for convenience.

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

Yes, in that I think it would be good to establish a clear convention here and stick to it. Whether the “Creatable” term is sufficiently clear to warrant a renaming of all the “Convertible” protocols, I’m not as sure about. I think at least CustomStringRepresentable and CustomDebugStringRepresentable would be worth doing since they imply a different direction from all the other “Convertible" protocols.

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

Yes, insofar as Swift generally seems to value predictability and consistency, and this would improve upon that.

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

The most relevant library here I think is the Cocoa libraries, as mentioned above, which are already using the term “representation” to mean a one-way conversion to another type.

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

I’ve been thinking about this for a while with regards to dictionary serialization, because it’s so common for data models, but I haven’t necessarily thought through all the implications for e.g. raw values.

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