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# Callback

- `Callback(callable $callback)`
- `Callback(callable $callback, mixed ...$arguments)`

Validates the input using the return of a given callable.

```php
v::callback(
    fn (int $input): bool => $input + ($input / 2) == 15,
)->assert(10);
// Validation passes successfully
```

## Templates

### `Callback::TEMPLATE_STANDARD`

| Mode       | Template                    |
| ---------- | --------------------------- |
| `default`  | {{subject}} must be valid   |
| `inverted` | {{subject}} must be invalid |

## Template placeholders

| Placeholder | Description                                                      |
| ----------- | ---------------------------------------------------------------- |
| `subject`   | The validated input or the custom validator name (if specified). |

## Categorization

- Callables

## Changelog

| Version | Description |
| ------: | ----------- |
|   0.3.9 | Created     |

---

See also:

- [Call](Call.md)
- [CallableType](CallableType.md)
- [DateTime](DateTime.md)
- [FilterVar](FilterVar.md)