Is there a way to ensure the lengths of two list arguments match?

[cueckoo]

Originally opened by @riceluxs1t in cuelang/cue#381

Foo :: {
l1: [...string]
l2: [...string]
}

I want to make sure that instances of Foo have equal numbers of strings specified for l1 and l2. Is this possible to express in cuelang?

[cueckoo]

Original reply by @verdverm in cuelang/cue#381 (comment)

We generally answer questions in Slack. You can join from this link: https://cuelang.org/community

You can with an extra field:

ex: {
  l1: [...string]
  l2: [...string]
  sameLength: len(l1) == len(l2)
  failWhenDifferent: true & sameLength
}

[cueckoo]

Original reply by @myitcv in cuelang/cue#381 (comment)

@verdverm the check field should really be a definition to avoid it being emitted:

ex: {
	l1: [...string]
	l1: ["test"]
	l2: [...string]
	l2: ["test"]
	sameLength :: len(l1) == len(l2)
	sameLength :: true
}

[cueckoo]

Original reply by @myitcv in cuelang/cue#381 (comment)

I'll close this issue because we've address the direct question. There is also plans for a constrain() built-in as part of the evaluator redesign in #338

[cueckoo]

Original reply by @verdverm in cuelang/cue#381 (comment)

@myitcv would hidden fields work equally as well?