Best way to allow one plugin to use anothers functions

[mvlcek]

I am wondering what the best method is to allow all installed plugins use a function from one plugin.
For my Multi User plugin I have 3 plugins that other plugins can use:

• add_mu_permission()
  
• check_user_permission()/*]
  
• check_user_permissions()
  

Now this worked fine when my blog plugin used add_mu_permission() to add permissions and the other two to retrieve them. However, I have another plugin of mine, named "lead_management" in which the mentioned functions do not work. They seem be not defined yet. If I try to check to see if they are undefined and define them, the multi user plugin would throw an error as it would be trying to re-declare the function.

First, all the functions in your plugins should use a plugin specific prefix/code, like add_mu_permission, check_mu_user_permission, check_mu_user_permissions.

Then any other plugin can use the functions with

Code:

if (function_exists('check_mu_user_permission')) check_mu_user_permission();

You can also encapsulate this call in a plugin specific function (with its own prefix/code) and use this function in your plugin (xyz = code for this plugin):

Code:

function check_xyz_user_permission() {
  if (function_exists('check_mu_user_permission')) { // Multi user plugin
    check_mu_user_permission();
  } else if (function_exists('check_emu_user_permission')) { // extended multi user plugin
    ...
  } else ...;
}

(better even to put all your non-public plugin functions in a class to minimize names in the global name space)

Just remember that the plugins are loaded in a random order (it depends on operating system, file system, etc.) thus

• do not call any other plugin's functions in the plugin initialization (outside any trigger or filter), as the other plugin might not be loaded yet
  
• do not try to redefine functions from other plugins but rather use another unique name, as the plugin might be loaded later on and will throw an error