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PHP - Why using "global" considered bad?

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−0

In PHP why is using global like in the example below considered bad?

$a = 1;

class foo
{
    public function bar()
    {
        global $a; // <-- Why is this considered bad?
    }
}

I want a concrete example(s) of what can go wrong with this code.

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It's not PHP specific (2 comments)

1 answer

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Nothing in particular will go wrong. global is a valid and supported keyword, the code will work. There is no problem for the computer.

The problem is for you. When something is global, it could be getting changed by anything else. You have to read through the whole codebase, to understand what exactly it's used for. If it's local, then it cannot be changed by things outside the local scope, which makes it a lot easier for a human brain to keep track of things.

This is the main thing wrong with global and it's not specific to PHP.

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