`is_a()` vs `is_subclass_of()`

_PHP is_a() vs is_subclass_of().md

PHP is_a() vs is_subclass_of()

<?php

class A {}

class B extends A {}

interface I {}

trait T {}

class C extends B implements I {
    use T;
}

Operation	is_a()	is_subclass_of()	instanceof
A of A	✅	❌	✅
A of B	❌	❌	❌
A of I	❌	❌	❌
A of T	❌	❌	❌
A of C	❌	❌	❌
B of A	✅	✅	✅
B of B	✅	❌	✅
B of I	❌	❌	❌
B of T	❌	❌	❌
B of C	❌	❌	❌
I of A	❌	❌	❌
I of B	❌	❌	❌
I of I	✅	❌	❌
I of T	❌	❌	❌
I of C	❌	❌	❌
T of A	❌	❌	❌
T of B	❌	❌	❌
T of I	❌	❌	❌
T of T	✅	❌	❌
T of C	❌	❌	❌
C of A	✅	✅	✅
C of B	✅	✅	✅
C of I	✅	✅	✅
C of T	❌	❌	❌
C of C	✅	❌	✅

composer.json

{
    "require": {
        "symfony/console": "^7.3"
    }
}

index.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 I
{
}

trait T {
}

class C extends B implements I {
    use T;
}

$classes = [
    'A',
    'B',
    'I',
    '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, $class2, true) ? '<fg=green>true</>' : '<fg=red>false</>',
            class_exists($class1) && (new $class1()) instanceof $class2 ? '<fg=green>true</>' : '<fg=red>false</>',
        ];
    }
}

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

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

$table->render();

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)

Small change, adding instanceof to the mix...
~ @gggeek

Let's add the check but also leave the initials.

#! /usr/bin/env 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) {
        $instanceOf = '';

        if (class_exists($class1)) {
            $instanceOf = (new $class1()) instanceof $class2 ? '<fg=green>true</>' : '<fg=red>false</>';
        }

        $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</>',
            $instanceOf,
        ];
    }
}

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

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

$table->render();

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

@serious-angel Done!

I even updated the display a bit :)