✨ Use generics for predicates #2265

nikola-jokic · 2023-04-07T13:36:12Z

k8s-ci-robot · 2023-04-07T13:36:20Z

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k8s-ci-robot · 2023-04-07T13:36:21Z

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k8s-ci-robot · 2023-04-07T13:36:22Z

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nikola-jokic · 2023-04-07T13:38:37Z

Hey @alvaroaleman 👋

I hope this is what you meant by using generics ☺️

alvaroaleman · 2023-04-08T20:22:13Z

pkg/predicate/predicate.go

 	return Funcs{
 		CreateFunc: func(e event.CreateEvent) bool {
-			return filter(e.Object)
+			v := e.Object.(T)


We still have the type assertion here and its possible to misuse this by constructing a predicate for the wrong type. What I'd want is the whole chain of source/predicate/handler using generics. I'll update the issue to clarify that

Update

The only thing I'm having trouble with is builder
Right now, builder can watch multiple resources and I can't really instantiate many watches with different type parameters using generics without providing a top level function and potentially changing the interface of the Watch method
I'm looking into ways of doing it, so the change is as minimal as possible

I looked into this some time ago. Golang doesn't support generic methods, which is why we can not keep assembling everything in the controller.Watch but instead have to provide predicate+handler in a constructor to the source

nikola-jokic · 2023-04-19T11:05:32Z

pkg/builder/controller.go

 	ctrl             controller.Controller
 	ctrlOptions      controller.Options
 	name             string
 }

+func newObjectPredicate[T client.ObjectConstraint](p predicate.Predicate[T]) predicate.Predicate[client.Object] {


This is heavily work in progress, but I wanted to push changes to make sure this approach is okay
Since controller is able to watch on multiple resources, the only way I could think of (since we can't use generic methods) is to create a generic function that will convert this generic type to a client.Object
That way, the complexity is internal, and we use client.Object interface internally. The caller still can leverage generics to use those types

The only thing is that the project needs to be go version 1.20, because they added interfaces to be comparable in that version

This does not work now, there are many tests where I'd have to provide types and similar
The controller watch is also something that needs to be changed or provided another method like controller.WatchType(WithWatch() that can be a generic function returning wrapped objects

Since many types can handle multiple types, wrapping them in interfaces was the only thing that I could think of to provide a nice API... Some types can be improved, but the only thing I wanted to ask is, is there a different approach I should take?

This is the issue I was referring to in #2265 (comment). We have to change how this works in order to accomodate generics. The source needs to get the handler and predicates at its construction time rather than at Start time, because using Start entails passing it through the controller and that would entail that we can only support one type per controller.

I see, I'll work on it

k8s-ci-robot · 2023-04-21T05:36:08Z

PR needs rebase.

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Use generics for predicates

cb3dbed

k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Apr 7, 2023

k8s-ci-robot added the needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. label Apr 7, 2023

k8s-ci-robot requested a review from FillZpp April 7, 2023 13:36

k8s-ci-robot requested a review from varshaprasad96 April 7, 2023 13:36

k8s-ci-robot added the size/S Denotes a PR that changes 10-29 lines, ignoring generated files. label Apr 7, 2023

alvaroaleman reviewed Apr 8, 2023

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Proposed way of handling generics

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k8s-ci-robot added size/XXL Denotes a PR that changes 1000+ lines, ignoring generated files. and removed size/S Denotes a PR that changes 10-29 lines, ignoring generated files. labels Apr 19, 2023

nikola-jokic marked this pull request as draft April 19, 2023 11:01

k8s-ci-robot added the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Apr 19, 2023

nikola-jokic commented Apr 19, 2023

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k8s-ci-robot added the needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. label Apr 21, 2023

nikola-jokic closed this Jul 10, 2023

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✨ Use generics for predicates #2265

✨ Use generics for predicates #2265

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k8s-ci-robot commented Apr 21, 2023

✨ Use generics for predicates #2265

✨ Use generics for predicates #2265

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k8s-ci-robot commented Apr 21, 2023