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Topic: Virtual method table

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July 23

	Delphi Q&A: What is the virtual-method table?
		The main purpose of the VMT is to hold pointers to a class’s virtual methods.
		To call a virtual method, then, a program first dereferences the object reference to get the VMT pointer, and then it dereferences that pointer at the offset corresponding to the desired method to determine the address of that method.
		Here resides a pointer to a list of pointers to the class’s dynamic methods (as opposed to its virtual methods, which are in the VMT itself).
	www.cs.wisc.edu /~rkennedy/vmt (778 words)

	Jikes RVM User's Guide -- Methods and Fields
		A virtual method dispatch entails loading the TIB pointer from the object reference, loading the address of the method body at a given offset off the TIB pointer, and making an indirect branch and link to it.
		Static method dispatch is simpler than virtual dispatch, since a well-known JTOC entry method holds the address of the compiled method body.
		Method slots in a TIB or the JTOC may hold either a pointer to the compiled code, or a pointer to the compiled code of the lazy method invocation stub.
	jikesrvm.sourceforge.net /userguide/HTML/userguide_28.html (503 words)

	Module17 C++ Polymorphism virtual functions late early binding virtual table
		The key elements that define a typical case of polymorphism are a base class and the descendants that inherit a base class's methods.
		In particular, the fanciest type of polymorphism involves virtual methods that are inherited from a base class.
		You will recall that the method named message() from the base class is available in the truck class because the method from the base class is inherited with the keyword public included in line 25 as shown below.
	www.geocities.com /mikerisan/Module17.html (1434 words)

	The Jikes Research Virtual Machine (RVM)
		A virtual method dispatch entails loading the TIB pointer at a fixed offset off the object reference, loading the address of the method body at a given offset off the TIB pointer, moving this address to the PowerPC "link-register," and executing a branch-and-link instruction -- four instructions.
		Method invocation stacks and the JTOC are the only two Jalapeño structures that violate the Java language requirement that arrays not contain both primitives and references.
		For nonfinal virtual method calls, the optimizing compiler predicts the receiver of a virtual call to be the declared type of the object.
	www-106.ibm.com /developerworks/java/library/j-jalapeno (13047 words)

	Virtual Methods (Site not responding. Last check: 2007-10-15)
		Calls to virtual methods are resolved at run time with delayed or late binding.
		By default the methods are static; virtual methods contain a special keyword virtual as part of their declaration.
		However, virtual method override must be done by a method that uses exactly the same syntax, e.g.
	www.tmt.com /helphtml/virtual_methods.htm (97 words)

	Delphi 5 Developer's Guide: Object-oriented programming for component writers (Site not responding. Last check: 2007-10-15)
		Virtual and dynamic methods, by contrast, use indirect means to look up the address of their methods at runtime, which takes somewhat longer.
		The address of a virtual method isn't determined at compile time; instead, the object where the method is defined looks up the address at runtime.
		When a method is declared as abstract in an ancestor class, you must surface it (by redeclaring and implementing it) in any descendant component before you can use the new component in applications.
	info.borland.com /techpubs/delphi/delphi5/dg/oop.html (2631 words)

	SQLite CVSTrac
		The virtual table mechanism allows an application to publish interfaces that are accessible from SQL statements as if they were tables.
		The arguments are passed as written (as text) into a constructor for the virtual table when the virtual table is created and the constructor is responsible for parsing and interpreting the arguments.
		Virtual table implementations that are built as loadable extensions for SQLite version 3.3.7 and earlier will need to be recompiled in order to work with SQLite versions 3.3.8 and later.
	www.sqlite.org /cvstrac/wiki?p=VirtualTables (1227 words)

	Pointers to virtual method tables
		Unlike plain vanilla methods, whose procedure addresses can be computed at compile time, the address of a virtual method may not be known until run time.
		This is a table containing flags used to describe the attributes of all of the selectors.
		Should the entry in the classes table corresponding to the segment number be non-nil the descriptor of the class owning that segment is obtained.
	www.dcs.gla.ac.uk /~wpc/reports/compression/node21.html (743 words)

	Virtual method table - Wikipedia, the free encyclopedia
		A virtual method table, virtual function table, dispatch table, or vtable, is a mechanism used in programming languages to support dynamic polymorphism, i.e., run-time method binding.
		Method calls are performed by fetching the method's address from the object's dispatch table.
		Note that a virtual call requires at least an extra indexed dereference, and sometimes a "fixup" addition, compared to a non-virtual call, which is simply a jump to a compiled-in pointer.
	en.wikipedia.org /wiki/Virtual_method_table (977 words)

	Delphi 5 Object Pascal Language Guide: Memory management (Site not responding. Last check: 2007-10-15)
		A method pointer is stored as a 32-bit pointer to the entry point of a method, followed by a 32-bit pointer to an object.
		The layout of a VMT is shown in the following table.
		A class-reference value is stored as a 32-bit pointer to the virtual method table (VMT) of a class.
	info.borland.com /techpubs/delphi/delphi5/oplg/memory.html (3108 words)

	how to get the VMT address of an event
		There is only one VMT per class (not one per instance), but two distinct class types never share a VMT, no matter how identical they appear to be.
		VMTs are built automatically by the compiler, and are never directly manipulated by a program.
		At positive offsets, a VMT consists of a list of 32-bit method pointers, one per user-defined virtual method in the class type, in order of declaration.
	www.elists.org /pipermail/delphi/2000-May/008978.html (525 words)

	Mechanism for dynamic selection of an object's method - Patent 6487714 (Site not responding. Last check: 2007-10-15)
		Associated with such a method for which different behavior is, or may be required during run-time, is a separate code block 20 and 21 each defining a different implementation of the method.
		At method invocation time, the pointer is used to go directly to the appropriate virtual method table, saving the indirection through the class and the array of virtual method tables.
		The pointer to the appropriate virtual method table is in addition to the pointer to the class object which is required for other operations.
	www.freepatentsonline.com /6487714.html (4919 words)

	Delphi in a Nutshell: Chapter 2: The Delphi Object Model
		Methods in the derived class refer to the derived class's field, and methods in the ancestor class refer to the ancestor's field.
		If the same method is declared in an ancestor class and in a derived class, Delphi calls the most-derived method, as shown in Example 2-4.
		The C++ term for an abstract method is a "pure virtual method." If you call a constructor for a class that has an abstract method, the compiler issues a warning, telling you that you probably made a mistake.
	www.oreilly.com /catalog/delphi/chapter/ch02.html (9089 words)

	Dr. Dobb's \| Multiple Inheritance for Delphi \| July 22, 2001
		Hence, if I call the virtual method Work in the TProgrammer part of TLead (through a reference returned by the cast function), it is not the overriding implementation in TLead that will be called, but rather the implementation in TProgrammer, since the superclass member m_ProgrammerSuperClass is of that class.
		Virtual methods that are not forwarded by the helper class are hidden and cannot be overridden in subclasses.
		The solution is to make TEmployee a virtual base class, which means that it is shared among the superclasses that inherit from it, so only one instance of it is included in the subclass; see Figure 3(b).
	www.ddj.com /184409973?pgno=6 (4215 words)

	Delphi tutorial - Writing your first component
		Virtual - When running all objects which already had created, all "method" with word "Virtual" will be in memory style FIFO or what we call VMT "Virtual method table".
		Dynamic and Virtual is slower than Static Method when running because it has to go though Method Table every time, but in a long term it will be faster for more memory space.
		Both methods Static and Virtual allow programmer to be able to manage his or her program better.
	www.sunncity.com /Tutorial/Writing_Your_First_Component01.html (1391 words)

	The ABCs Of OOP - Part 3 (Site not responding. Last check: 2007-10-15)
		Virtual methods are one of the most useful and powerful features of object-oriented programming.
		With virtual methods you can plug and play with the methods of a class without having to know how or when those particular methods are called.
		There is a small performance penalty associated with using virtual methods, since the system must maintain a virtual method table (VMT), or list of methods, so it knows at runtime which methods to call under which situation (this is an example of "late" binding).
	www.clarionmag.com /cmag/v1/v1n5abcsofoop_part3.html (2694 words)

	Call graph construction by profiling
		In normal lazy method compilation, the code stub captures the first invocation of a method without distinguishing callers.
		The TIB entry of a method is replaced by an array of instruction addresses.
		The lazy method compilation code stub is extended to a profiling code stub which, in addition to triggering the lazy compilation of the callee, also generates a new call edge event from the caller to the callee.
	www.usenix.org /events/vm04/tech/full_papers/qian/qian_html/node5.html (308 words)

	Interpreters and Compilers
		As classes are loaded into the run-time virtual machine (Java is an object-oriented language), the method pointers in the virtual method table, which in the interpreted version of Java would point to the bytecode of the corresponding methods, are replaced with pointers to the JIT compiler.
		The pointer in the virtual method table is then patched to point to the native-code version of the method so that future calls to the method will jump to the native-code.
		As long as the average size of an individual method tends to be rather small, the wait is not likely to be noticeable.
	www.cs.wustl.edu /~plezbert/contcom/thesis/node6.html (923 words)

	C++Builder, 1, Borland C++Builder White Paper: Application Development with C++Builder and Delphi
		This is the simplest method for accessing Automation Objects, and it is the one you should use unless speed is an extremely important issue for you.
		If the methods weren't declared virtual, then there would be no virtual method table, and the ploy would not work.
		The names of the methods you want to call are not important to the C++ implementation; all that matters is the order in which the methods are declared.
	dn.codegear.com /article/10105 (1732 words)

	OOP - Ready for Take Off - What they do not teach you in class (Site not responding. Last check: 2007-10-15)
		A virtual method is the ability to "call up" or "out" to derived methods.
		In Clarion, a virtual method is one that is defined in both a base class and a derived class.
		This makes the methods and properties from a class visible to only those methods and properties that are derived from it.
	www.clarionmag.com:8080 /col/97-11-oop.html?pFriendly=true (3351 words)

	[No title] (Site not responding. Last check: 2007-10-15)
		Dynamic Binding: --done on virtual objects In C++ : At compile time, each class, either super or derived would create a static virtual method table lookup.
		And each derived class would contain the virtual method table content of its parent class.
		In Java: The equivalent of virtual method table in Java is the Method Lookup Table.
	userpages.umbc.edu /~iadebo1/codes/June205 (238 words)

	Three Myths About Turbo Pascal
		Myth number two: Since you can't assign object methods to procedural variables, you can't call methods indirectly (that is, through a pointer).
		When you make a virtual call, TPW expects the virtual method table to be in the current data segment.
		It's important to note that it's not enough to merely avoid explicitly making virtual calls: Calling a static method that ultimately calls a virtual method is just as dangerous.
	www.midnightbeach.com /jon/pubs/3myths.htm (1701 words)

	Khiron Software (Site not responding. Last check: 2007-10-15)
		This table contains the entry point of all virtual methods, to be late bound at run-time.
		Finally the compiler creates a RTTI table entry for each identifier, which provides information on it's type (from ordinal types, and sub types, to Classes), defined in Typinfo.int along with routines for converting Enumerated types into their Design-Time representations and vice-versa, and routines for Getting and Setting properties by Name.
		This routine is used by the Delphi application to bind the physical memory address of form delegation methods from the Method Name exported in Stream information to physical components created from the stream.
	www8.pair.com /rmorris/rtti.htm (3626 words)

	Polymorphism, pthreads, multi-threading, and libstdc++ - C++
		Virtual methods lose their virtual-ness property in a constructor (and a
		Virtual methods must work in a destructor, as all good programming
		The VMT is not reliably set to the correct table until
	www.thescripts.com /forum/thread63766.html (650 words)

	List of object-oriented programming terms - Wikipedia, the free encyclopedia
		Pure virtual function (also called pure virtual method)
		Virtual function pointer (also called virtual method pointer)
		Virtual table (also called vtable, virtual function table or virtual method table)
	en.wikipedia.org /wiki/List_of_object-oriented_programming_terms (152 words)

	VTAM - Virtual Table Access Method, Virtual Telecommunications Access Method
		Virtual Table Access Method is not the only word formed from VTAM.
		(Virtual Telecommunications Access Method) The software component that controls communications in SNA networks.
		Virtual Telecommunications Access Method: a set of program that control communication between nodes and applications programs running on a host system.
	www.auditmypc.com /acronym/VTAM.asp (224 words)

	Virtual File Systems (Site not responding. Last check: 2007-10-15)
		Each filesystem type will have a virtual method table
		And it registers the method table in a global kernel data structure
		Sometimes a method will be 'inherited' from the generic version
	perl.plover.com /yak/ext2fs/samples/slide010.html (103 words)

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