- Indirection
In
computer programming , indirection is the ability to reference something using a name, reference, or container instead of the value itself. The most common form of indirection is the act of manipulating a value through itsmemory address . For example, accessing avariable through the use of apointer . A stored pointer that exists to provide a reference to an object by double indirection is called an "indirection node". In some older computer architectures, indirect words supported a variety of more-or-less complicatedaddressing mode s.Object-oriented programming makes use of indirection extensively, a simple example beingdynamic dispatch . Higher-level examples of indirection are the design patterns of the proxy and theproxy server . Delegation is another classic example of an indirection pattern. In strongly-typedinterpreted language s with dynamicdatatype s, most variable references require a level of indirection: first the type of the variable is checked for safety, and then the pointer to the actual value is dereferenced and acted on.Recursive types are usually implemented using indirection because otherwise if a value of a datatype can contain the entirety of another value of the same datatype, there is no limit to the size a value of this datatype could need.When doing symbolic programming from a formal mathematical specification the use of indirection can be quite helpful. To start with a simple example the variables x, y and z in an equation such as z = square root (x squared + y squared) can refer to any number. One could imagine objects for various numbers and then x, y and z could point to the specific numbers being used for a particular problem. The simple example has its limitation as there are infinitely many real numbers. In various other parts of symbolic programming there are only so many symbols. So to move on to a more significant example, in logic the formula α can refer to any formula, so it could be β, γ, δ, ... or η→π, ς v σ,.... When
set-builder notation is employed the statement Δ={α} means the set of all formulae - so although the reference is to α there are two levels of indirection here, the first to the set of all α and then the second to a specific formula for each occurrence of α in the set Δ.Indirection occurs also in
linguistics , especially inagglutinative languages , such as theFinnish language orTurkish language Fact|date=September 2008.ee also
* Handle
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