PHP, methods, functions, and the global scope

It’s funny. Even after nearly 10 years with the language, there are still little gotchas that sometimes get me. I ran across one today.

Say you have two objects, and the look like this:

<?php
class ObjA {
    public static function test() {
        global $test;
        var_dump($test);
    }
}

class ObjB {
    public static function test() {
        $test = 1;
        ObjA::test();
    }
}

ObjB::test();
?>

It doesn’t work. You get NULL.

Say I were to do something like this:

<?php
class ObjB {
 public static function test() {
     $test = 1;
     global $test;
     var_dump($test);
 }
}

ObjB::test();
?>

You also get NULL. And this:

<?php
function a() {
    $test = 1;
    b();
}

function b() {
    global $test;
    var_dump($test);
}

a();
?>

Also fails.

The reason is that the global scope on PHP is just that: global. Any time you’re in a function or method, you’re in a local scope and all local scopes are independent of each other. So you can’t global in something from one local scope to another. Variables are either global or local.

That much I get and makes sense (and is in the documentation). What threw me for a loop was that PHP won’t copy something into the global scope from a local scope that is already defined **and will happily overwrite your local scope with a null value from the global scope if one doesn’t exist in the global scope, **in the process of creating the variable in the global scope. If you want a variable in the local scope to be global, you have to declare it as global before you write a value to it.

Or, to put it another way:

<?php
class ObjA {
    public static function test() {
        global $test;
        var_dump($test);
    }
}

class ObjB {
    public static function test() {
        global $test;
        $test = 1;
        ObjA::test();
    }
}

ObjB::test();
?>

Works beautifully.

Did something I wrote help you out?

That's great! I don't earn any money from this site - I run no ads, sell no products and participate in no affiliate programs. I do this solely because it's fun; I enjoy writing and sharing what I learn.

All the same, if you found this article helpful and want to show your appreciation, here's my Amazon.com wishlist.

Read More

Monitoring for Filesystem Changes using PHP and Laravel

Let’s say you have a Laravel application that does some data processing, and you want to monitor a directory for incoming changes, that you can then process using queued jobs. There are a couple of ways you could do something like this. You could scan those directories on a schedule using a cronjob. It’s doable. But what happens if you want to monitor a few thousand directories for changes? You can use tools like incron. Also doable, but another dependency. But what if I told you you could do it all with PHP. And within Laravel, no less?

New Open Source Code

Launched two new pieces of open source code in the last couple of months. PlayerControls PlayerControls is a macOS Cocoa framework that creates a View containing playback controls for media like videos or sounds. It is written in pure Swift 4 and has no dependencies. SearchParser SearchParser is a parser that converts a freeform query into an intermediate object, that can then be converted to query many backends (SQL, ElasticSearch, etc). It includes translators for SQL (using PDO) and Laravel Eloquent ORM. It supports a faceted language search as commonly found on many sites across the web. It is written in modern PHP. Both are licensed under the MIT license. Go check them out on Github.