Dynamic types, part 2

In a previous lesson on dynamic types we've learned that a variable can hold a values of any type and that type may change during the runtime.

There is even more. Array keys should be a string either an integer. However values of the same array can hold anything: strings, booleans, integers, floats, functions, resources, or another (nested) arrays. This is a totally fine PHP array:

$wow_array =
[
    4 => 'This is a string',
    'cat' => [25 => false, 0 => function() use(&$a) { return 10; }],
    17 => [true, 42.347, [], 'four', [true, fopen('text.txt', 'r')]],
    'dog' =>
    [
        'plus' => function($a, $b)
        {
            return $a + $b;
        },
        7485 => null,
        'yohoho' => socket_create(AF_UNIX, SOCK_STREAM, 0)
    ]
];

Look at this line of code:

$foo(10, 'Todd');

Is this a valid line of code? It is, if $foo is a function. But is it a function? We don't know! We will find this out when the control flow reach this line, and not earlier.

You could get a type of a variable with gettype function. However you should use it for a debug purpose only. Using it as a part of a program logic is a bad software design (except absolutely rare cases).

$a = [1, 2, 3];
echo gettype($a); # Prints "array"