I believe 'summary' is obsolete, and you're supposed to use Custom[Debug]StringConvertible to customize your type's reporting now.
-Joe > On Dec 29, 2015, at 10:38 PM, Austin Zheng via swift-evolution > <[email protected]> wrote: > > Hi all, > > I'd like to gauge reaction for a proposal I was considering: adding to the > standard library's Mirror type a 'summary' property, and the option to > initialize a Mirror with a custom summary. If no custom summary is provided, > the summary would default to the string produced by calling > String(reflecting: subject) on the subject at the time of mirror creation. > > Some context: right now, there are two APIs for mirrors in the standard > library: CustomReflectable, which is publicly exposed and relies on the > conforming type creating a Mirror object, and _Reflectable, which relies on > the conforming type having a companion type conforming to _MirrorType. A > short-term goal is to migrate the standard library's types off the > _Reflectable API and have them use the CustomReflectable API, and changing > dump() accordingly. > > The extant implementation of dump() uses a property on _MirrorType called > "summary". (This is where e.g. "4 elements" comes from when you dump() an > array.) "summary" is absent from Mirror or any types related to > CustomReflectable. I asked Joe Groff about this and the rationale was that it > was deemed too similar to debugDescription (or String(reflecting: foo)) to be > worth carrying over. > > I would like to suggest that there might be a purpose for "summary": > > - Types with children, especially container types like arrays, often print > out a description of their children as part of their debugDescription or > description, redundant when using an API like dump() which provides a > structural representation of the children of the subject. In such cases a > lighter-weight description (like "3 elements") might be more appropriate to > represent to the user. > > - Certain types like CGRect don't conform to CustomStringConvertible, > CustomDebugStringConvertible, Streamable, etc. Having a custom summary for > these types customized by the corresponding Mirror would allow for a 'pretty' > representation during reflection in lieu of the ugly one generated by the > runtime without making more substantial changes to the API which might break > third-party code (such as conforming CGRect to any of the aforementioned > protocols). > > I know that Mirror (and reflection as a whole) are being considered for major > design changes, so this would be a minor transient change to make the API > easier to work with in the meantime. > > Please let me know whether or not you think this proposed change is > meaningful and worthwhile, or if you have any questions. > > Best, > Austin > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________ swift-evolution mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-evolution
