respect-validation/docs/validators/KeyOptional.md
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<!--
SPDX-FileCopyrightText: (c) Respect Project Contributors
SPDX-License-Identifier: MIT
-->
# KeyOptional
- `KeyOptional(string|int $key, Validator $validator)`
Validates the value of an array against a given validator when the key exists.
```php
v::keyOptional('name', v::stringType())->assert([]);
// Validation passes successfully
v::keyOptional('name', v::stringType())->assert(['name' => 'The Respect Panda']);
// Validation passes successfully
v::keyOptional('email', v::email())->assert([]);
// Validation passes successfully
v::keyOptional('email', v::email())->assert(['email' => 'therespectpanda@gmail.com']);
// Validation passes successfully
v::keyOptional('age', v::intVal())->assert(['age' => 'Twenty-Five']);
// → `.age` must be an integer value
```
The name of this validator is automatically set to the key name.
```php
v::keyOptional('age', v::intVal())->assert(['age' => 'Twenty-Five']);
// → `.age` must be an integer value
```
## Note
This validator will pass for anything that is not an array because it will always pass when it doesn't find a key. If you
want to ensure the input is an array, use [ArrayType](ArrayType.md) with it.
```php
v::arrayType()->keyOptional('phone', v::phone())->assert('This is not an array');
// → "This is not an array" must be an array
```
Below are some other validators that are tightly related to `KeyOptional`:
- To validate if a key exists, use [KeyExists](KeyExists.md) instead.
- To validate an array against a given validator requiring the key to exist, use [Key](Key.md) instead.
## Templates
## Template placeholders
| Placeholder | Description |
| ----------- | ---------------------------------------------------------------- |
| `subject` | The validated input or the custom validator name (if specified). |
## Categorization
- Arrays
- Structures
## Changelog
| Version | Description |
| ------: | :------------------------- |
| 3.0.0 | Created from [Key](Key.md) |
## See Also
- [ArrayType](ArrayType.md)
- [ArrayVal](ArrayVal.md)
- [Each](Each.md)
- [Key](Key.md)
- [KeyExists](KeyExists.md)
- [Property](Property.md)
- [PropertyExists](PropertyExists.md)
- [PropertyOptional](PropertyOptional.md)
[array]: https://www.php.net/array
[ArrayAccess]: https://www.php.net/arrayaccess