Multiple modules overriding same core file in Magento

Question

How does Magento handle multiple modules overriding the same core file? Is it possible? How is it done?

Answer 1

You have 3 choices for resolving conflicts:

• Merge the code from one conflicting file into another and switch off the rewrite config.xml in one
• Switch off the rewrite in one config.xml and then make the conflicting extension PHP file extend the other extension
• Use the <depends> capability to make one extension depend on another. They will then rewrite in that order

Example (option # 2)

class A_Extension_Model_Type_Onepage extends Mage_Checkout_Model_Type_Onepage

You would change it to:

class A_Extension_Model_Type_Onepage extends B_Extension_Model_Type_Onepage

Read more @ http://www.webshopapps.com/blog/2010/11/resolving-magento-extension-conflicts/