# XO0305: `_` arm hides variants of an enum declared in this module

Warning. An unguarded `_` or catch all binding arm on an enum declared in the same module hides the variants it covers, so adding a variant later compiles silently instead of failing at every `match`. List the variants (an or pattern such as `B | C` keeps it short). Enums from other modules, the prelude (`Option`, `Result`), and non enum values may use `_`, since their owners can add variants. A `_` arm that hides at least 8 variants and more than half of the enum is a deliberate default and is not reported (decision 0080). See core 3.5.

## Example

```xo
enum E { A, B, C }

fn f(e: E) -> Int {
  match e {
    A => 1
    _ => 2
  }
}
```

## Fix

```xo
enum E { A, B, C }

fn f(e: E) -> Int {
  match e {
    A => 1
    B | C => 2
  }
}
```

Run `xo explain XO0305` for this text in a terminal, or see
[section 10.6 of the specification](../../spec/core/#106-diagnostic-codes).