WordPress at a glance
function is not described

WP_REST_Request::set_param() public WP 4.4.0

Sets a parameter on the request.

If the given parameter key exists in any parameter type an update will take place, otherwise a new param will be created in the first parameter type (respecting get_parameter_order()).

{} It's a method of the class: WP_REST_Request{}

No Hooks.

Return

Null. Nothing.

Usage

$WP_REST_Request = new WP_REST_Request();
$WP_REST_Request->set_param( $key, $value );
$key(string) (required)
Parameter name.
$value(mixed) (required)
Parameter value.

Changelog

Since 4.4.0 Introduced.

Code of WP_REST_Request::set_param() WP 5.5.3

<?php
public function set_param( $key, $value ) {
	$order     = $this->get_parameter_order();
	$found_key = false;

	foreach ( $order as $type ) {
		if ( 'defaults' !== $type && is_array( $this->params[ $type ] ) && array_key_exists( $key, $this->params[ $type ] ) ) {
			$this->params[ $type ][ $key ] = $value;
			$found_key                     = true;
		}
	}

	if ( ! $found_key ) {
		$this->params[ $order[0] ][ $key ] = $value;
	}
}