- var_dump: documentation ( source)
<?php
$row = new stdClass;
$field_name = 'field_my_field';
$delta = 0;
$row->$field_name = [];
$row->$field_name[$delta] = 'value'; // This works just fine.
$f = $field_name . ':title';
$row->$f = [$delta => 'value']; // This doesn't work.
var_dump($row);