How does one prevent nested function calls?

Question

First question, please forgive me if I do something wrong or this is a duplicate, I couldn't find another question similar.

I'm writing a very basic translater function i18n($string1) that, when given $string1, queries an index. If the string matches something in the index, it returns the translation $string2. If $string1 doesn't exist in the index, a new entry is created in the index that the user can later write a translated $string2 into.

The issue I want to try and solve is that a sloppy developer (me) might accidentally make a call i18n(i18n($string1)). The way this resolves is that the inner call finds $string1 in the index, returns $string2, then passes that to the function again which tries to find $string2 in the index. This would fail because $string2 is the translation and it would prompt the user to translate the translation... which isn't helpful.

I believe what I want is, in the case that the function is called nested within itself, it returns the string $string1. Thus, it doesn't matter how many times I call i18n within itself, it always translates the string $string1.

What is the best way to do this? I considered using a static or global $isCalled variable, or a singleton, but I've been told in the past that these solutions are almost certainly evil and there's probably something better.

Thanks in advance!

Answer 1

You have been told right.

You could go by analyzing the debug_backtrace(), but that is really time and ressources consuming. Also it is an not needed overhead of the translation function.

If a developer calls the translation function with an already translated string it is the developers responsibility to fix that problem not the softwares.

A way to avoid this double calling is to use PHP_CodeSniffer and define coding standars which would forbid such usage. It would be though tough to check for those things if both functions are not in the same line.