`is_a()` vs `is_subclass_of()`

_PHP is_a() vs is_subclass_of().md

PHP is_a() vs is_subclass_of()

To compute the results, just use Melody and run the script:

melody run https://gist.github.com/Pierstoval/ed387a09d4a5e76108e60e8a7585ac2d

melody.php

<?php
<<<CONFIG
packages:
    - "symfony/console: ^4.1"
CONFIG;

use Symfony\Component\Console\Helper\Table;
use Symfony\Component\Console\Helper\TableStyle;
use Symfony\Component\Console\Output\ConsoleOutput;

require __DIR__.'/vendor/autoload.php';

class A
{
}

class B extends A
{
}

interface It
{
}

trait T {
}

class C extends B implements It {
    use T;
}

$classes = [
    'A',
    'B',
    'It',
    'T',
    'C',
];

$rows = [];

foreach ($classes as $class1) {
    foreach ($classes as $class2) {
        $rows[] = [
            $class1.' of '.$class2,
            is_a($class1, $class2, true) ? '<fg=green>true</>' : '<fg=red>false</>',
            is_subclass_of($class1, $class2, true) ? '<fg=green>true</>' : '<fg=red>false</>',
        ];
    }
}

$table = new Table(new ConsoleOutput());

$table->setHeaders(['Operation', 'is_a()', 'is_subclass_of()']);
$table->setRows($rows);

$table->render();

output.txt

+-----------+--------+------------------+
| Operation | is_a() | is_subclass_of() |
+-----------+--------+------------------+
| A of A    | true   | false            |
| A of B    | false  | false            |
| A of It   | false  | false            |
| A of T    | false  | false            |
| A of C    | false  | false            |
| B of A    | true   | true             |
| B of B    | true   | false            |
| B of It   | false  | false            |
| B of T    | false  | false            |
| B of C    | false  | false            |
| It of A   | false  | false            |
| It of B   | false  | false            |
| It of It  | true   | false            |
| It of T   | false  | false            |
| It of C   | false  | false            |
| T of A    | false  | false            |
| T of B    | false  | false            |
| T of It   | false  | false            |
| T of T    | true   | false            |
| T of C    | false  | false            |
| C of A    | true   | true             |
| C of B    | true   | true             |
| C of It   | true   | true             |
| C of T    | false  | false            |
| C of C    | true   | false            |
+-----------+--------+------------------+

Small change, adding instanceof to the mix

foreach ($classes as $class1) {
    if ($class1 == 'It' || $class1 == 'T') {
        continue;
    }
    $obj1 = new $class1();
    foreach ($classes as $class2) {
        $rows[] = [
            $class1.' of '.$class2,
            is_a($obj1, $class2, true) ? '<fg=green>true</>' : '<fg=red>false</>',
            is_subclass_of($obj1, $class2, true) ? '<fg=green>true</>' : '<fg=red>false</>',
            $obj1 instanceof $class2 ? '<fg=green>true</>' : '<fg=red>false</>',
        ];
    }
}

In case anyone is wondering about the result: instanceof gives the same results as is_a. It is marginally faster, but it is also more limited in scope (it only accepts an instance as first argument and not a string, and does not accept a variable value as 2nd argument)