List functions?

[bigkevmcd]

I've implemented a couple of functions in projects that use CEL the easiest to link to is in Tekton Triggers:

https://github.com/tektoncd/triggers/blob/b133ef7b0d689c78a342879411a78c74b89de1f5/pkg/interceptors/cel/triggers.go#L202-L207

These are .first() and .last() which return the first and (unsurprisingly) last elements of a list.

This is useful when you want to split a string and take the first (or last) element in that list in a single expression, without having to resplit and calculate the length.

Would these be useful to add to the list extension?

I'm happy to do the work for this.

[TristonianJones]

Hi, I'd be totally happy to accept first() and last(). It's possible you'll want to use CEL's OptionalTypes() feature to indicate that the first and last might be absent in an empty list?

[TristonianJones]

Sorry for the delayed reply. I don't always see discussions right away.

[bigkevmcd]

I've got this working, but something that occurs to me, is the cel.OptionalTypes() might not be registered.

In this case...

lists_test.go:95: env.Check(![].first().hasValue()) failed: ERROR: <input>:1:21: undeclared reference to 'hasValue' (in container 'google.expr.proto2.test')
             | ![].first().hasValue()
             | ....................^

So, I added optional support for Optionals 😄