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When discussing sealed classes, the term "virtual function table" is mentioned quite frequently. What exactly is this? I read about a method table a while ago (I don't remember the purpose of the purpose of this either) and a google/search on here brings up C++ related results.
Thanks
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V-tables (or virtual tables) are how most C++ implementations do polymorphism. For each concrete implementation of a class, there is a table of function pointers to all the virtual methods. A pointer to this table (called the virtual table) exists as a data member in all the objects.
A virtual table is an object that presents an SQL table interface but which is not stored in the database file, at least not directly. The virtual table mechanism is a feature of SQLite that allows SQLite to access and manipulate resources other than bits in the database file using the powerful SQL query language.
A virtual table contains one entry for each virtual function that can be called by objects of the class. Each entry in this table is simply a function pointer that points to the most-derived function accessible by that class.
A vtable is simply an array of function pointers. The slots in the array correspond to the methods of of a class. Since methods are fixed per class, we do not have to maintain an array of functions for each object. Rather, it suffices to declare one vtable array per class.
The "virtual function table" or "virtual method table" is a list of method pointers that each class has. It contains pointers to the virtual methods in the class.
Each instance of a class has a pointer to the table, which is used when you call a virtual method from the instance. This is because a call to a virtual method should call the method associated with the class of the actual object, not the class of the reference to the object.
If you for example have an object reference to a string:
object obj = "asdf"; and call the virtual method ToString:
string text = obj.ToString(); it will use the String.ToString method, not the Object.ToString method. It's using the virtual method table of the String class (which the pointer in the string instance is pointing to), not the virtual method table of the Object class.
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The C# virtual function table works basically the same as the C++ one, so any resources which describe how the C++ virtual function table works should help you pretty well with the C# one as well.
For example, Wikipedia's description is not bad.
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