respect-validation/docs/rules/Key.md

# Key

- `Key(mixed $key)`
- `Key(mixed $key, Validatable $rule)`
- `Key(mixed $key, Validatable $rule, bool $mandatory)`

Validates an array key.

```php
$dict = [
    'foo' => 'bar'
];

v::key('foo')->validate($dict); // true
```

You can also validate the key value itself:

```php
v::key('foo', v::equals('bar'))->validate($dict); // true
```

Third parameter makes the key presence optional:

```php
v::key('lorem', v::stringType(), false)->validate($dict); // true
```

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

## Categorization

- Arrays
- Nesting
- Structures

## Changelog

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

***
See also:

- [ArrayVal](ArrayVal.md)
- [Attribute](Attribute.md)
- [Each](Each.md)
- [KeyNested](KeyNested.md)
- [KeySet](KeySet.md)
- [KeyValue](KeyValue.md)