<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div><blockquote type="cite" class=""><div class="">On Jan 10, 2018, at 2:10 PM, Connor Wakamo <<a href="mailto:cwakamo@apple.com" class="">cwakamo@apple.com</a>> wrote:</div><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class="">What is the use-case for a type conforming to this protocol but returning nil? If there is a use case for that, why not have such an implementation return “self” instead?</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Riley and Saagar answered this down-thread, but to confirm — returning nil would allow some instances of a type to use the “default” playground logging presentation while others use an alternate presentation instead.</div></div></div></div></blockquote><div><br class=""></div><div>Right, this gets back to the question: what is the use case for this? When would a type want to “sometimes” replace the default representation?</div><div><br class=""></div><div>It seems to me that a type author either wants to take control of presentation or not. While I’m sure we could imagine some use case for the behavior you’re describing, is it big enough to make it worth complicating the API?</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class=""><br class=""></div><div class="">This isn’t handled by `return self` because, unless I’m mistaken, there’s no way to detect that from the caller’s side (e.g. with two `Any` values, I can’t do `self === self.playgroundRepresentation`). </div></div></div></div></blockquote><div><br class=""></div><div>Ok</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class="">In short, can we change playgroundRepresentation to return Any instead of Any?. Among other things, doing so could ease the case of playground formatting Optional itself, which should presumably get a conditional conformance to this. :-)</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">I don’t think we can change this to return `Any` instead of `Any?`. I think there are potentially cases where a developer might want to selectively opt-in to this behavior.</div></div></div></div></blockquote><div><br class=""></div>Which cases? How important are they?</div><div><br class=""></div><div><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class="">I also don’t think that `Optional` would get a conditional conformance to this. I’m not proposing that any standard library or corelibs types gain conformances to this protocol. Instead, it’s up to a playground logger (such as PlaygroundLogger in <a href="https://github.com/apple/swift-xcode-playground-support" class="">swift-xcode-playground-support</a>) to recognize these types and handle them accordingly. The playground logger would look through the `Optional` so that this would effectively be true, but ideally the log data generated by a logger would indicate that it was wrapped by `Optional.some`.</div></div></div></div></blockquote><div><br class=""></div><div>Why not? I understand that that is how the old algorithm worked, but it contained a lot of special case hacks due to the state of Swift 1 :-). This is a chance to dissolve those away.</div><div><br class=""></div><div>To be clear, I would expect that the conformance for optional would be defined in the playground module along with this protocol - it wouldn’t be defined in the standard library itself.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class=""><br class=""></div><div class=""><div class="">One possibility would be to change the API so that it returns an enum. Imagine:</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>enum PlaygroundLoggingBehavior {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>/// Asks the playground logger to generate the standard logging for `self`.</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>case standard</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>/// Asks the playground logger to generate logging for the given `Any` instead of `self`.</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>case custom(Any)</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>}</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>protocol CustomPlaygroundLoggable {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>/// Returns the `PlaygroundLoggingBehavior` to use for `self`.</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>var playgroundLoggingBehavior: PlaygroundLoggingBehavior { get }</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>}</div><div class=""><br class=""></div><div class="">(To Saagar’s point in another email — you could even add a `case none` to PlaygroundLoggingBehavior to inhibit logging of a particular instance.)</div><div class=""><br class=""></div><div class="">`CustomPlaygroundLoggable` would be a little clunkier to implement than `CustomPlaygroundRepresentable` is, as in the common case folks would have to write `return .custom(…)`. It’s possible that the clarity and additional flexibility this grants outweighs that cost; I’m not sure, and would love feedback on that.</div></div></div></div></div></blockquote><div><br class=""></div><div>I just don’t understand the usecase for “conditional customizing” at all. By way of example, we don’t have the ability to do that with CustomStringConvertible. What is different about this case?</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><blockquote type="cite" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, "Liberation Mono", Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""><span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> Implementors of `CustomPlaygroundRepresentable` may return a value of one of</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> the above types to also receive a specialized log representation.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> Implementors may also return any other type, and playground logging will</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> generated structured logging for the returned value.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"></span><span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">public</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">protocol</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(111, 66, 193);">CustomPlaygroundRepresentable</span> {
</pre></div></div></div></blockquote><div class="">On the naming bikeshed, the closest analog to this feature is CustomStringConvertible, which is used when a type wants to customize the default conversion to string. As such, have you considered CustomPlaygroundConvertible for consistency with it?</div><div class=""><br class=""></div><div class="">The only prior art for the word “Representable” in the standard library is RawRepresentable, which is quite a different concept.</div><div class=""><br class=""></div><blockquote type="cite" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(36, 41, 46); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"; font-size: 16px; background-color: rgb(255, 255, 255);"><pre style="box-sizing: border-box; font-family: SFMono-Regular, Consolas, "Liberation Mono", Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 0px; word-wrap: normal; padding: 16px; overflow: auto; line-height: 1.45; background-color: rgb(246, 248, 250); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal;" class=""> <span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> Returns the custom playground representation for this instance, or nil if</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> the default representation should be used.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);">///</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> If this type has value semantics, the instance returned should be</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"></span> <span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"><span class="pl-c" style="box-sizing: border-box;">///</span> unaffected by subsequent mutations if possible.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(106, 115, 125);"></span> <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">var</span> playgroundRepresentation<span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 92, 197);">Any</span><span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">?</span> { <span class="pl-k" style="box-sizing: border-box; color: rgb(215, 58, 73);">get</span> }
</pre></div></div></div></blockquote><div class="">Again to align with CustomStringConvertible which has a ‘description’ member, it might make sense to name this member “playgroundDescription”.</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">I’m definitely open to different names for this. (`CustomPlaygroundRepresentable` was inspired by the API I’m removing, `CustomPlaygroundQuickLookable`, as they both take their sole property and make them -able.)</div><div class=""><br class=""></div><div class="">I do like the `playgroundDescription` name for the property, but am a little hesitant to use the name `CustomPlaygroundConvertible` because conforming types can’t be converted to playgrounds. I can’t come up with an appropriate word in `CustomPlaygroundThingConvertible` to use in place of `Thing`, though. (If we end up pivoting to the enum I described above then something like `CustomPlaygroundLoggable` would be more appropriate.)</div></div></div></div></blockquote><br class=""></div><div>I would strongly recommend aligning with the state of the art in CustomStringConvertible (which has been extensively discussed) and ignore the precedent in the existing playground logging stuff (which hasn’t).</div><div><br class=""></div><div>-Chris</div><div><br class=""></div><br class=""></body></html>