Way to determine object type in .cue

[cueckoo]

Originally opened by @vnzongzna in cuelang/cue#518

I need to determine if a value will of type struct or list to make the decision on adding new fields in it.
For example

sample: [...] | {...}
sample: batman: is: "back"
if sample == [...]  {
   array: "yes" 
}
if sample == {...} {
   struct: "yes" 
}

[cueckoo]

Original reply by @vnzongzna in cuelang/cue#518 (comment)

I got my solution here in slack. which pointed to checking against bottom. So a possible solution is

sample: [...] | {...}
sample: batman: is: "back"
if ( sample & [...]  )!= _|_ {
   array: "yes" 
}
if ( sample & {...}  )!= _|_ {
   struct: "yes" 
}

While this solution does work would it make sense to have an inbuilt function to return them?

[cueckoo]

Original reply by @vnzongzna in cuelang/cue#518 (comment)

Because as the author of the whole config I do know the possible values sample will have but maybe in a big enough configuration getting help from build-in will be faster.

[cueckoo]

Original reply by @mpvl in cuelang/cue#518 (comment)

While this solution does work would it make sense to have an inbuilt function to return them?

I think it may make sense to have a builtin for that. A more general builtin to make this nicer could be something like defined(sample&[...]) or even subsumes([...], sample). Both would be more consistent with values being types, and provide provide a larger range of possibilities.