# Key

- `Key(int|string $key, Rule $rule)`

Validates the value of an array against a given rule.

```php
v::key('name', v::stringType())->isValid(['name' => 'The Respect Panda']); // true

v::key('email', v::email())->isValid(['email' => 'therespectpanda@gmail.com']); // true

v::key('age', v::intVal())->isValid([]); // false
```

You can also use `Key` to validate nested arrays:

```php
v::key(
    'payment_details',
    v::key('credit_card', v::creditCard())
)->isValid([
    'payment_details' => [
        'credit_card' => '5376 7473 9720 8720',
    ],
]); // true
```

The name of this validator is automatically set to the key name.

```php
v::key('email', v::email())->assert([]);
// message: email must be present

v::key('email', v::email())->assert(['email' => 'not email']);
// message: email must be valid email
```

## Note

* To validate if a key exists, use [KeyExists](KeyExists.md) instead.
* To validate an array against a given rule if the key exists, use [KeyOptional](KeyOptional.md) instead.

## Templates

## Template placeholders

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

## Categorization

- Arrays
- Nesting
- Structures

## Changelog

| Version | Description                                                          |
|--------:|----------------------------------------------------------------------|
|   3.0.0 | Split by [KeyExists](KeyExists.md) and [KeyOptional](KeyOptional.md) |
|   0.3.9 | Created                                                              |

***
See also:

- [ArrayVal](ArrayVal.md)
- [Each](Each.md)
- [KeyExists](KeyExists.md)
- [KeyOptional](KeyOptional.md)
- [KeySet](KeySet.md)
- [Property](Property.md)
- [PropertyExists](PropertyExists.md)
- [PropertyOptional](PropertyOptional.md)