cue eval -c structs.cue
cmp stdout expect-stdout-cue

-- frontmatter.toml --
title = "Structs"
description = ""

-- text.md --
Struct is the most important composite type in CUE.
It's members are called fields.

A struct field may be optional.
One can use an optional field to indicate what the type should be if it were
specified.
A regular (or required) field, on the other hand, must be made concrete
for a configuration to be converted to, say, JSON.

It is okay for an optional field to be bottom (`_|_`).
This just means that field may not be specified.

-- structs.cue --
#a: {
    foo?: int
    bar?: string
    baz?: string
}
b: #a & {
    foo:  3
    baz?: 2  // baz?: _|_
}

-- expect-stdout-cue --
b: {
    foo: 3
}