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I notice that in some plugins you can override functions by ...

  1. Creating an uploads folder
  2. Creating a folder with the plugin name
  3. Using the following code

    if (!function_exists('function_name')) {
        function function_name() {

Is this standard for all Wordpress plugins or only if they're written in a specific way?

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up vote 1 down vote accepted

If the plugin displays content via any function, the code:

if(!function_exists('function_name')) function_name();

... is used for safety.

If your plugin is disabled, and the if (!function_exists('function_name')) is missing, your theme will throw a fatal error.

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ah I see...thanks! – redconservatory Jul 26 '11 at 14:46
This isn't actually correct. The OP is referring to wrapping the function definition in a if( ! function_exists() ) conditional, not the actual function call in the template. – Chip Bennett Jul 26 '11 at 15:00
Yes, but his wording is not the best. The wrapping is done for theme safety only, and not for overriding WordPress functions. – Ciprian Jul 26 '11 at 15:12

These are referred to as pluggable functions, and are intended to be able to be over-ridden, either by Plugins, Themes, or Child Themes.

It is only standard for functions that are intended to be over-ridden - and, generally speaking, the better practice is to add filter hooks to function outputs, rather than making functions pluggable.

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