Magic Constants

Magic Constants

Magic Constants and Printing Values for Debugging

Magic constants are filled in by the compiler from where they appear: __LINE__, __FILE__, __DIR__, __FUNCTION__, __CLASS__, __METHOD__, __NAMESPACE__, __TRAIT__ and __PROPERTY__ (PHP 8.4, inside a property hook only). Product::class gives the fully qualified class name. The workhorse is __DIR__: require __DIR__ . '/config.php' works from any directory.

Magic constants in a namespaced class (shop/src/Catalog/Product.php)PHP

<?php
namespace Shop\Catalog;
final class Product
{
    public string $sku = 'bk-7' { get => __PROPERTY__ . '=' . strtoupper($this->sku); }
    public function report(): void
    {
        echo __METHOD__, ' | ', __FUNCTION__, ' | ', self::class, "\n";
        echo $this->sku, ' | ', basename(__FILE__), ':', __LINE__, ' | ', __DIR__, "\n";
    }
}
(new Product())->report();

Output

Shop\Catalog\Product::report | report | Shop\Catalog\Product
sku=BK-7 | Product.php:11 | /tmp/ch04-02/shop/src/Catalog

To see what a variable holds, print_r() reads best but prints false and null as nothing, var_dump() shows every type and length, and var_export() prints PHP you can paste into a test. print_r($order, true) returns the text instead, ready for error_log(). var_dump and VarDumper goes further.

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