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Most modern processors have special hardware support for subroutine "call" and "return" instructions, so the overhead of one extra machine instruction per dispatch is somewhat diminished. Anton Ertl, the Gforth compiler's co-creator, stated that "in contrast to popular myths, subroutine threading is usually slower than direct threading". [ 10 ]
In object-oriented programming languages that support virtual methods, the compiler will automatically create a dispatch table for each object of a class containing virtual methods. This table is called a virtual method table or vtable , and every call to a virtual method is dispatched through the vtable.
The C++ standards do not mandate exactly how dynamic dispatch must be implemented, but compilers generally use minor variations on the same basic model. Typically, the compiler creates a separate virtual method table for each class.
The default form of dispatch is static. To get dynamic dispatch the programmer must declare a method as virtual. C++ compilers typically implement dynamic dispatch with a data structure called a virtual function table (vtable) that defines the name-to-implementation mapping for a given class as a set of member function pointers. This is purely ...
Compilers generate initial instruction sequences for the VLIW CPU in roughly the same manner as for traditional CPUs, generating a sequence of RISC-like instructions. The compiler analyzes this code for dependence relationships and resource requirements. It then schedules the instructions according to those constraints.
It is a form of method dispatch, which describes how a language or environment will select which implementation of a method or function to use. [1] Examples are templates in C++, and generic programming in Fortran and other languages, in conjunction with function overloading (including operator overloading).
Originally known as transfer vector, this method is also more recently known under such different names as "dispatch table" or "virtual method table" but essentially performing exactly the same purpose. This pointer function method can result in saving one machine instruction, and avoids the indirect jump (to one of the branch instructions).
Multiple dispatch is used much more heavily in Julia, where multiple dispatch was a central design concept from the origin of the language: collecting the same statistics as Muschevici on the average number of methods per generic function, it was found that the Julia standard library uses more than double the amount of overloading than in the ...