Question

I understand that the underscore _ is an acceptable character for naming variables / functions / classes etc. However I was wondering if there are any other special characters which can be used. I tested out a few with no luck and have assumed for a long time that there are not, however I figured I would see if anyone else knows for certain. This would be mostly for aesthetic purposes, however I imagine a special character naming convention would be useful when working with other developers to define value types etc.

Answer 1

If you check the docs on variables it says that:

Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: ‘[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*’

But basically people have agreed to only use a-zA-Z0-9_ and not the “fancy” names since they might break depending in the encoding one uses.

So you can have a variable that is named $aöäüÖÄ but if you save that with the wrong encoding you might run into trouble.

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The same goes for functions too btw.

So

function fooööö($aà) { echo $aà; }

fooööö("hi"); // will just echo 'hi'

will just work out (at least at first).

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Also check out:

Exotic names for methods, constants, variables and fields - Bug or Feature?

for some discussion on the subject.