# XO0535: `.debug()` inside an interpolation

Reported by `xo vet`, not `xo check`. `${expr:?}` interpolates the Debug text of expr, the same text as `expr.debug()`, so `${xs.debug()}` is `${xs:?}`. The diagnostic carries the fix (in `xo vet --json`), which replaces `.debug()` with `:?`. A type's own `debug` method is left alone. See core 1.6 and decision 0296.

## Example

```xo
fn show(xs: List[Int]) -> Str {
  "items ${xs.debug()}"
}
```

## Fix

```xo
fn show(xs: List[Int]) -> Str {
  "items ${xs:?}"
}
```

Run `xo explain XO0535` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).