Saagar Jha
> On Jan 10, 2018, at 14:10, Connor Wakamo <cwak...@apple.com> wrote:
>
>> On Jan 10, 2018, at 12:39 PM, Saagar Jha <saa...@saagarjha.com
>> <mailto:saa...@saagarjha.com>> wrote:
>>
>> Well, in my experience performance issues tend to come not from trying to
>> display a single object, but when you have an aggregation of many objects.
>> For example, displaying one Int is pretty lightweight, as is an [Int] with a
>> handful of elements, but displaying an [Int] with million elements is not
>> (this is assuming that collections will run the playgroundRepresentation on
>> their individual elements as they do currently). I don’t think the current
>> proposal can solve this issue as it’s pitched currently. (For those curious,
>> this doesn’t have a good solution today, either: the best “solution” I’ve
>> been able to come up with is to move performance-sensitive out into a
>> Playground’s Sources folder, which isn’t displayed.)
>
> Yes, this proposal does not affect this case: the playground transform will
> still instrument all of the source code in the main source file. This
> proposal is merely about deprecating/removing a substandard API for
> controlling how values are presented in playgrounds with a better, more
> flexible one. (Though see my other reply to Chris where I present an
> alternative which could be extended to include support for disabling logging
> altogether for an instance.)
>
>> Fundamentally, I don’t think it’s clear what the “default” value is supposed
>> to be: we already have three different interpretations of what it could do:
>> do literally nothing (i.e. display an empty representation), use a
>> superclass’s representation, or use a structural representation based on
>> whether the type is an enum, struct, class, etc. I think we need to clear up
>> what the default actually means (and if we even need it at all) before we
>> can proceed.
>
> This API is a bit wishy-washy as to what the “default” is. That’s somewhat
> intentional — the default presentation of an arbitrary Swift value/object is
> defined by the IDE, not by an API in Swift. I think my terminology is a bit
> confused here, and I’ll try to address that in a revision of the proposal.
> Let me try to clarify this a bit:
>
> The fundamental design of playgrounds is that the compiler will insert calls
> to a logging function which is effectively required to take an `Any`. So
> therefore every instance of every type must be loggable by the playground
> logger. The PlaygroundLogger framework in swift-xcode-playground-support
> <https://github.com/apple/swift-xcode-playground-support> implements this by
> generating either structured log entries using `Mirror` or specialized,
> opaque (aka IDERepr) log entries. PlaygroundLogger will generate a structured
> log entry for most instances, but for instances of special types it knows
> about (e.g. String, Int, NSColor, UIView, etc.) it will generate an opaque
> log entry which an IDE can then consume and display as is appropriate.
>
> The CustomPlaygroundRepresentable API I’ve proposed does exactly one thing:
> it allows instances of conforming types to provide an optional stand-in to be
> used by the playground logger. So PlaygroundLogger would handle the following
> cases thusly:
>
> - If a type conforms to CustomPlaygroundRepresentable and returns a
> non-nil value, PlaygroundLogger will generate the appropriate log entry for
> the returned value
> - If a type conforms to CustomPlaygroundRepresentable and returns nil,
> PlaygroundLogger will generate the appropriate log entry for `self`
> - If `self` is one of the types (or a subclass of one of the
> types) for which PlaygroundLogger generates an opaque entry, PlaygroundLogger
> will generate an opaque log entry
> - Otherwise, PlaygroundLogger will generate a structured log
> entry
Just wanted to make it totally clear here: is the superclass selected the one
that is the closest to the current type, or the one that is the most distant
parent? Referring back to the example I had further upthread:
class FooView: UIView {
override var playgroundRepresentation: Any? {
return “foo”
}
}
class BarView: FooView {
override var playgroundRepresentation: Any? {
return nil
}
}
Does BarView show up as a UIView, or a FooView? If it’s shown as a FooView,
then returning nil is superfluous: you can just not override
playgroundRepresentation and it’ll pick up the one from FooView.
>
> This process if potentially recursive (likely up to an implementation-defined
> limit): if `Foo: CustomPlaygroundRepresentable` and `Bar:
> CustomPlaygroundRepresentable`, and a `Foo` instance returns an instance of
> `Bar` from `playgroundRepresentation`, then the playground logger should
> effectively log `self.playgroundRepresentation.playgroundRepresentation`.
>
> Connor
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