As you might be already familiar WP-FastEndpoints allows you to fetch request data via function arguments, and optionally
you can validate that data via type-hinting.

Built-in type-hints

By default, when you rely on built-in PHP types, DateTime, DateTimeInterface or when no type-hint is used,
WP-FastEndpoints will look for the data in the url or in the query parameters, in this order. However, if desired this
behaviour can be changed via #[Attributes].

<?php
$router->get('/posts', function (int $ID) {
    // Your logic
});

<?php
use Attributes\Wp\FastEndpoints\Options\Header;

$router->get('/user', function (#[Header('Authorization')] string $token) {
    // Your logic
});

The following is a list of all those type-hints:

• bool
• int
• float
• string
• callable
• array
• object
• DateTime
• DateTimeInterface

Custom classes

For more complex types of data structures we can rely on custom classes. If you know how to write a class you know how
to validate a request in WP-FastEndpoints.

By default, when you rely on type-hints from custom classes WP-FastEndpoints will look for the data either in the
JSON or body of the current request. However, as with built-in type-hints, this behaviour can be changed via #[Attributes].

<?php
class HelloWorld {
    public string $name;
}

<?php
$router->post('/hello', function (HelloWorld $hello) {
    // Your logic
});

<?php
use Attributes\Wp\FastEndpoints\Options\Url;    
use Attributes\Wp\FastEndpoints\Options\Query;

$router->post('/hello', function (#[Url, Query] HelloWorld $hello) {
    // Your logic
});

How to type-hint arrays?

Unfortunately, PHP doesn’t provide a way to properly type-hint array’s. Dictionaries aren’t an issue because custom classes
can be used, but for sequenced arrays is a bit more tricky.

To solve this issue, WP-FastEndpoints assumes that any ArrayObject
child class should be considered a typed-hint array. However, to actually type-hint that array a property name $type
with a type-hint needs to be specified in the class. Otherwise, an array of mixed is assumed.

<?php
class HelloArr extends ArrayObject {
    public Hello $type;
}

$router->get('/say-hello', function (HelloArr $allHellos) {
    foreach ($allHellos as $hello) {
        echo "Hello $hello->name!";   
    }
});

Special classes

When an argument has a type-hint it usually means that the request payload should follow that class structure. However,
there are three special classes which don’t follow this pattern:

• WP_REST_Request - Can be used to retrieve the
  current request
• WP_REST_Response - Can be used to retrieve
  the response to be sent to the client, in case of a success. You could change the response HTTP status code or the data
  which is sent to the client (wouldn’t recommend the last one though).
• Endpoint - The current endpoint
  instance. You shouldn’t ever need this one.

<?php
$router->get('/request', function (WP_REST_Request $request) {
    return $request->get_params();
});

<?php
$router->get('/response/204', function (WP_REST_Response $response) {
    $response->set_status(204);
});

Required vs optional properties

Until now, we have seen most how to specify required properties from a request payload. In case your property is optional
you can rely on default values for that, like the following.

<?php
$router->get('/required', function (int $id) {
    return $id;
});

<?php
$router->get('/optional', function (int $id = 0) {
    return $id;
});

<?php
$router->get('/payload/optional', function (?HelloWorld $hello = null) {
    return $hello ? $hello->name : "No payload";
});