[Kwiver-users] Fwd: [Kwiver-announce] Best practices for passing inherited types through Sprokit Pipeline

[Matthew Leotta]

I’d rather not tell sprokit to ignore type checking on some subset of types, but not others.  However, equivalently you could define all track_set types to be “track_set” regardless of the specific derived class.  Then each process would need to check at run time if the track_set it got can be down cast to the type it was expecting.  That approach is equivalent, but probably less of a hack.  It’s still not ideal.

—Matt

> On Nov 15, 2017, at 2:01 PM, Brian Clipp <brian.clipp at kitware.com> wrote:
> 
> Agreed.  Matt P. had an interesting suggestion.  What if Sprokit's graph type checking would allow some potentially wrong graphs through to allow for up-casting?  It could catch really egregious issues, e.g. int passed into a port expecting a string, but not subtle issues like a track_set passed into a feature_track set port where the track set is in fact an object_track_set.  
> Basically, the type checker would consider up-casts and down-casts as being equivalent types.  Most errors would be caught at pipeline construction time but a few might only be caught at run-time.
> 
> -Brian
> 
> 
> On Wed, Nov 15, 2017 at 1:53 PM Matthew Leotta <matt.leotta at kitware.com <mailto:matt.leotta at kitware.com>> wrote:
> This has been a long standing issue with sprokit, from what I recall.  It seems to me that we need a mechanism for allowing sprokit type checking to allow for casting up the inheritance hierarchy.  A feature_track_set is a track_set, so any process that can process a track_set should also be able to process a feature_track_set.  I’m not sure if there is an easy way of checking this because I think sprokit just does string name comparison for type checking.  Maybe the type name strings could be “track_set”, “track_set.feature”, “track_set.object” and we could do substring comparison?  Anyway, that is probably a discussion for another day.  In your case, the issue is more challenging because there is also down casting involved.  Ideally you want to encode that the input and output types for this process must be 1) the same exact type and 2) a track_set or some derivative of it.  I’m not sure that we can do that in sprokit yet.
> 
> I mostly agree with the best practices rules in the PPTX, except that I’d like to see sprokit improved so that the first rule is not needed.  For now, I think your Option 2 (slide 4) makes the most sense.
> 
> —Matt
> 
> 
>> On Nov 15, 2017, at 1:22 PM, Brian Clipp <brian.clipp at kitware.com <mailto:brian.clipp at kitware.com>> wrote:
>> 
> 
>> Pushing the tread over to kwiver-users.  I attached the original ppt.
>> 
>> -Brian
>> 
>> ---------- Forwarded message ---------
>> From: Matthew Leotta <matt.leotta at kitware.com <mailto:matt.leotta at kitware.com>>
>> Date: Wed, Nov 15, 2017 at 1:08 PM
>> Subject: Re: [Kwiver-announce] Best practices for passing inherited types through Sprokit Pipeline
>> To: Matt Phillips <matt.phillips at kitware.com <mailto:matt.phillips at kitware.com>>, Brian Clipp <brian.clipp at kitware.com <mailto:brian.clipp at kitware.com>>
>> Cc: <kwiver-announce at public.kitware.com <mailto:kwiver-announce at public.kitware.com>>
>> 
>> 
>> Guys,
>> 
>> Let’s take this discussion to the kwiver-users list rather than kwiver-announce.  kwiver-annouce is supposed to be for major announcements, like new versions.
>> 
>> Of course this make me wonder if we really need kwiver-announce anymore.  Is there anyone on this mailing list who is not also on kwiver-users and who only wants to receive very infrequent notifications about KWIVER releases and other major announcements?  If this describes you, please send me a response privately.  If I get no responses in a week or so, I think we should retire this list and use only kwiver-users.  That pattern aligns better with what our other open source projects do for mailing lists.
>> 
>> Thanks,
>> Matt
>> 
>> 
>>> On Nov 15, 2017, at 12:56 PM, Matt Phillips <matt.phillips at kitware.com <mailto:matt.phillips at kitware.com>> wrote:
>>> 
>>> Is the issue here just slicing when derived class objects are passed to Keyframe selector?  I'm not familiar off the top of my head with how sprokit does serialization/deserialization but might making that 'slice-proof' be the answer?  By e.g. storing type information and using factory methods at construction.
>>> 
>>> Matt
>>> 
>>> On Wed, Nov 15, 2017 at 12:46 PM, Brian Clipp <brian.clipp at kitware.com <mailto:brian.clipp at kitware.com>> wrote:
>>> Hi All.
>>> 
>>> I ran into a case yesterday where I had a process that output a child class and a process that expected an input from it of the parent class.  Sprokit's type checking fails in that case.  It lead me to spend some time thinking about what types to pass between processes.  After some discussion with Aaron and Matt B. these are some suggestions I've arrived at.  
>>> 
>>> Thoughts?
>>> 
>>> Brian
>>> 
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> 
>> <Inherited Types in Sprokit Pipelines.pptx>_______________________________________________
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