Source

File: wp-includes/rest-api.php

function rest_validate_array_contains_unique_items( $array ) {
	$seen = array();

	foreach ( $array as $item ) {
		$stabilized = rest_stabilize_value( $item );
		$key        = serialize( $stabilized );

		if ( ! isset( $seen[ $key ] ) ) {
			$seen[ $key ] = true;

			continue;
		}

		return false;
	}

	return true;
}