Optional values and narrowing

Unobin checks null strictly. A value of type optional(T) cannot be used where T is required until the source accounts for null.

Declaring optional values

inputs: {
  greeting: { type: optional(string) }
  tls:      { type: optional(object({ cert: optional(string) })) }
}

A declaration default provides a value when the input is omitted. For an optional declaration, null follows the same default path:

size: { type: optional(integer), default: 3 }

Null tests

A null test narrows the value where the test proves it is set:

banner: if input.greeting == null then 'hello' else input.greeting

The else branch sees input.greeting as string.

Guarded navigation

Use ?. to read through a maybe-null object:

input.tls?.cert

The result is still optional. Use ?? to provide a fallback:

input.tls?.cert ?? 'self-signed'

Comprehension filters

A when filter can narrow element fields:

[ for u in input.upstreams : u.port when u.port != null ]

Constraint guards

A constraint can use when to guard the require expression:

{
  kind:    predicate
  when:    input.upstreams != null
  require: @core.all([ for u in input.upstreams : u.port == null || u.port > 0 ])
  message: 'upstream ports must be positive'
}