# `syntax.optional_chaining`

Field of a missing value read with `?.`.

Area 2, [Values and types](../topics/values-and-types.md); not declinable; the next step is usually the agent's.

A field of a value that may be `none` is read in a `match` too.

```jadpo
type ShippingCode = Text {
    max_length: 10
}

type Address = Object {
    postal_code: ShippingCode
}

type Customer = Object {
    address: Address?
}

function postal_code(customer: Customer) -> ShippingCode? {
    return customer.address?.postal_code
}
```

```text
error: Jadpo reads a value that may be `none` with `match`, not `?.`
 --> main.jadpo:14:28
   |
14 |     return customer.address?.postal_code
   |                            ^^ write a `match`
  reason: `?.` reads a field of a value that may be missing in JavaScript, TypeScript, C#, Kotlin and Swift; Jadpo reads a value that may be `none` with a `match` that handles both cases.
  next: Write `match customer.address` with the arms `some(address) -> address.postal_code` and `none -> none` (agent)
  rule: syntax.optional_chaining
  help: https://jadpo.dev/docs/errors/syntax.optional_chaining

check failed: 1 error, 1 file
```