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

-- frontmatter.toml --
title = "Closed structs"
description = ""

-- text.md --
Struct is the most important composite type in CUE.

A struct may be open or closed.
A closed struct may only be merged with structs that have fields that
it defines to be allowed.
In other words, closing a struct is equivalent to requiring that all
other values be undefined.

A closed struct can be created using the `close` builtin,
but are more commonly defined using a _definition_, defined next.

-- structs.cue --
a: close({
    field: int
})

b: a & {
    feild: 3
}

-- expect-stdout-cue --
a: {
    field: int
}
b: _|_ // field "feild" not allowed in closed struct