List of one or more elements?

[cueckoo]

Originally opened by @NReilingh in cuelang/cue#835

I'd like to vet a schema that requires one or more elements in a list. My schema is:

prop: [...#MyType]

and I want to guarantee that prop is NOT [].

I am very new to CUE, so I may not be defining these correctly in the first place. Is there a language feature that can help me do this cleanly, or is this the same problem described in cuelang/cue#401?

I can accomplish this functionally with:

#checkLength: len(prop) > 0
#checkLength: true

...but this does not result in a helpful error message. list.MinItems(prop, 1) has the same problem.

[cueckoo]

Original reply by @myitcv in cuelang/cue#835 (comment)

Thankfully the world has moved on since that question/question, and the new evaluator which will land in v0.3.0 (please do use the latest beta) support this:

package x

import "list"

#MyType: int

prop: list.MinItems(2) & [...#MyType]
prop: [5]

If you cue eval the above to test you get:

prop: invalid value [5] (does not satisfy list.MinItems(2)):
    ./x.cue:7:7
    ./x.cue:7:21

[cueckoo]

Original reply by @eonpatapon in cuelang/cue#835 (comment)

For minimum items in a list you can also express it like this:

l: [string, string, ...string]

Where l should be a list of at least 2 string values.