note 107748 added to language.oop5.interfaces

dlovell2001's example does not quite get it right either. Both interfaces and classes provide abstraction. His example would be better implemented as an abstract class than an interface. The distinction between the two is that an abstract class says what an object is and describes its visible appearance. An interface describes the visible appearance without restricting what the object may be. Whether the Database is an SQL database, an Oracle database, or some other type of database, it is still a database - a particular kind of object. In this case, the description should be an abstract class - class because it is a database, abstract because the class is useless without knowing just what kind of database it is. On the other hand, consider the iterator. The object may be an array, a json string, a filesystem directory tree, a database result set, the infinite set of prime numbers, a random number generator, etc. While these are all different objects, they share in common the fact that they have a first value and that each value will be followed by another until a last value is reached, if ever. These are all different types of objects, so different classes, but share a common way of accessing these values. This is where you use an interface. Use abstract classes to declare the common method signatures of related classes. Use interfaces to declare the common method signatures of unrelated classes. And while we are here, once you have 5.4, use parent classes to define the common methods and properties of related classes and traits to define the common methods and properties of unrelated classes. ---- Server IP: 192.41.42.26 Probable Submitter: 75.132.154.20 ---- Manual Page -- http://www.php.net/manual/en/language.oop5.interfaces.php Edit -- https://master.php.net/note/edit/107748 Del: integrated -- https://master.php.net/note/delete/107748/integrated Del: useless -- https://master.php.net/note/delete/107748/useless Del: bad code -- https://master.php.net/note/delete/107748/bad+code Del: spam -- https://master.php.net/note/delete/107748/spam Del: non-english -- https://master.php.net/note/delete/107748/non-english Del: in docs -- https://master.php.net/note/delete/107748/in+docs Del: other reasons-- https://master.php.net/note/delete/107748 Reject -- https://master.php.net/note/reject/107748 Search -- https://master.php.net/manage/user-notes.php