Is it possible to declare empty variable in PHP?

https://www.virendrachandak.com/demos/php-isset-vs-empty-vs-is_null.php

Solution:

PHP doesn't have an explicit statement to initialise variables, like Javascript'svar. PHP variables get initialised when they're first assigned to. It's a design choice, for better or worse. To create a variable you always have to assign something to it. Since a variable must have some value and PHP's value for "nothing" isnull, you want:

$variable = null;
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(Alternative ways to create variables exists, like references, e.g.:parse_str($foo, $bar); var_dump($bar);, but let's leave that aside.)

Thevar statement exists in Javascript to determine scope; Javascript has nested scopes and needs an explicit initialisation to determine what a variable's scope is. Scoping in PHP works differently and doesn't have that ambiguity, hence such a separate statement isn't necessary. Originally PHP also liked implicit globals a lot (a terrible idea in hindsight), which somewhat clashes with the idea of explicit initialisation statements in the first place.

var $var; (a variable declared, but without a value)

That is an incomplete/incorrect quote, it should be "a variable declared but without a value in a class", since that's the only place thevar keyword can be used.

As an example, Python also uses initialisation-by-assignment, and also has nested scope. It uses a different approach to resolve this:

foo = 42

def bar():
    foo = 69

    def baz():
        nonlocal foo
        foo = 2
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The rule in Python is, that a variable is local to a function if any assignment is done to the variable inside the function. So thefoo = 69 creates a new local variable insidebar here. To allow assignment to the variable from an inherited scope, thenonlocal orglobal keyword must be used to explicitly denote that variable as inherited.foo = 2 here reassignsfoo = 69, but neither reassignsfoo = 42.

Solution:

There is novar keyword which works the same way as in javascript. From w3schools:

Note: Unlike other programming languages, PHP has no command for declaring a variable. It is created the moment you first assign a value to it.

Your other question:

If it's not possible, is there any logical explanation why it wasn't implemented in PHP?

One logical explanation could be that in PHP all variables start with a$ symbol. So PHP immediately knows when something is a variable and not a function or keyword, without the need for a declaration.

In fact, javascript code also works without declarations, but here, they are still recommended in most cases.

If you want to declare a variable and set its value tonull in PHP, just use:

$myVar = null;
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Solution:

In class context you can make it without explicitnull:

class BarClass {
    private FooClass $foo;
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As simple variable, you can't. Use$variable = null (or do not write it at all). As all not set vars are null by default:

$var1 = null;

var_dump(isset($var1), empty($var1), is_null($var1));
// bool(false), bool(true), bool(true)

var_dump(isset($var2), empty($var2), is_null($var2));
// Notice:  Undefined variable: var2 - From `is_null`
// bool(false), bool(true), bool(true)

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