In order to write future-proof code, it is recommended that you don't place many variables, functions or classes in the global namespace. This will prevent naming conflicts with 3rd party code as well as possible future additions to the language.
One common way to prevent naming conflicts of functions and classes is to add them to their own dedicated namespace.
<?php
namespace MyProject;
function my_function() {
return true;
}
\MyProject\my_function();
This still needs you to keep track of already used namespaces, but once you have decided on a namespace you will be using you can add all functions and classes to it without having to think about conflicts again.
It is considered best practice to limit the number of variables added to the global scope in order to prevent naming conflicts with 3rd party code.
Note: Variable scoping
Because of PHP's scoping rules variables defined inside functions and methods are not in the global scope and as such cannot conflict with other variables defined in the global scope.