Implementing plugin overrides

Plugin overrides (requires Q2A 1.5+) can replace or wrap over 150 functions defined within the Q2A core. Overrides can be very powerful, but they run a risk of incompatibility with future versions of Q2A. If possible, it is recommended to use modules or layers instead. Nonetheless, some things can only be done via overrides, and future versions of Q2A will try not to break them.

Not all functions in Q2A can be overridden. To check a particular function, see whether its definition begins with:

if (qa_to_override(__FUNCTION__))

Functions are overridden by redefining them in a PHP file in your plugin directory, then calling qa_register_plugin_overrides() with the name of that file in qa-plugin.php. Here is a simple example of a PHP file which overrides qa_retrieve_url():

<?php

function qa_retrieve_url($url)
{
    // implement some specialized code for retrieving a URL's contents
}

In Q2A, overrides go beyond simple function replacement by allowing you to call through to the original Q2A function from within your own function. To call the original function, simple add _base to its name. For example:

<?php

function qa_retrieve_url($url)
{
    if (substr($url, 0, 8)=='https://')
        // specialized code for retrieving secure pages
    else
        return qa_retrieve_url_base($url);
}

When overriding functions, you should call through to the _base function as much as possible. This allows you to deal with special cases and modify inputs and outputs without replacing a function in its entirety. If multiple plugins override the same function and call through to _base, Q2A will automatically build a calling chain of appropriately renamed functions, each of which calls the next. This process takes place in qa_load_override_files() in qa-base.php and is transparent to you as a plugin developer. Overall, using the _base function will maximize the chance of your plugin working well with other plugins, as well as future versions of Q2A.