Can I set a value conditionally based on the existence of an optional field?

[NReilingh]

I would like to define a struct that accomplishes the following:

#Type {
  optional?: string
  result: bool
  result: <if optional is set then true else false>
}

Is this possible?

[mpvl]

With the API or in CUE directly?

In CUE directly you can write:

#Type: {
	optional?: string
	result: optional != _|_
  }
  a: #Type
  a: optional: "foo"

Comparing against bottom is not specified in the spec, or at the very least it is poorly defined. I've written (but still need to publish) a relatively minor change, replacing this with builtins like isdefined(optional). But for now this works.

In the API you can do a LookupPath and see whether the resulting value exists.

[NReilingh]

In CUE directly, yes -- this works! I almost got there on my own, but was comparing with _ instead of bottom. Thanks!

[cueckoo]

This discussion has been migrated to cue-lang/cue#887.

For more details about CUE's migration to a new home, please see cue-lang/cue#1078.