How does plugin system work (wordpress, mybb ...)?

Question

I'm curious how plugins work, I just know that instead of changing the code we use plugins, but how do they do their job without changing the code ? and what should a coder consider when coding a new project so it can have plugins ? and thank you very much :D

Answer 1

There are multiple variations on how to implement a plugin system. Wordpress uses a quite common scheme often described as "hooks." I don't know the exact implementation but it basically works like this:

// plugin.php script registers its own callback function
register_plugin("hook_type", "plugin_function_123");

function plugin_function_123($params) { ... }

Where the hook_type is often an action name or something. And when the main application runs through a specific point (or e.g. needs some data processsed) it invokes all registered callback functions:

$output = call_plugins("hook_type", $param1, $param2);

This is often implemented behind the scenes as a simple loop:

foreach ($registered_plugins[$action] as $func) {
    $func($param1, $param2, ...);   // or call_user_func_
}

Now it depends on the hook/action type what parameters are present, and if any result text is expected. There are also differences in parameter passing (e.g. some callbacks require &$var references). And some plugin systems rely on objects instead (if not as many varying action types exist or more complex structures are to be worked with).