RE: [PHP] What is the practical use of "abstract" and "interface"?

[snip] "enforcing a contract" is a lot of maningless gobbledegook. The simple fact is that it is possible to have an interface without ever using the term "interface". Nothing extra is added by using the term "interface" (except for effort) so there is absolutely no advantage in doing so. That is why I say that the term "interface" is a waste of effort as absolutely nothng is gained. [/snip] What about encapsulation? Also, there is an advantage to interfaces that has not been mentioned yet, the fact that a class can implement multiple interfaces (polymorphism). And yes, I know that I can extend by inheritance to create polymorphism too, but what is the most efficient method? It depends on the application. Like anything else interfaces are a tool and there may be multiple tools that can accomplish the same job (i.e. table saw, band saw, hand saw). Pick the one that is right for you.