Pointer Metaprogramming

OK, I admit it... I'm posting this page mainly to be ornery^H^H^H^H^H^Hplay the DevilsAdvocate. (The fact that this disclaimer is necessary just goes to show how well-received this topic is likely to be.) But given that DevilsAdvocate is a fun and productive game to play (and I firmly believe that the world would be a better place if more people looked at the other side of issues rather than merely basking in their own self-assuredness), here is my (latest) attempt to shove a stick into the pot and stir the proverbial hornet's nest.

PointerMetaprogramming is the practice, commonly found in languages such as CeeLanguage and CeePlusPlus, of using techniques such as PointerArithmetic, forced typecasts, and other forms of (hopefully) ImplementationDefined behavior in order to engage in MetaProgramming. Not all forms of PointerMetaprogramming necessarily require use of pointer operations; but most do involve pointers at some level.

PointerMetaprogramming is a very powerful metaprogramming technique, as it allows the programmer to manipulate program data in unlimited ways; ways typically disallowed by the facilities present in most high-level languages. Many types of systems programs (including the runtime systems for most high-level languages) require use of PointerMetaprogramming; which is why one seldom encounters (for example) a JavaVirtualMachine which is written in Java.

PointerMetaprogramming is also a controversial technique (like many other techniques for MetaProgramming), it is often alleged that many programmers lack the skill/training to do it correctly. PointerMetaprogramming is often subjected to the following criticisms:

AlternateHardAndSoftLayers is a good way to partition a program into those parts which need the power of PointerMetaprogramming, and those which do not (and can be written in a higher-level language).

Key techniques of PointerMetaprogramming:

Several languages support PointerMetaprogramming "out of the box".

Other languages allow it, but only in distinguished code modules (those marked as "unsafe" or with some other pejorative keyword).

Others disallow it completely, like JavaLanguage. (However, even languages which disallow PointerMetaprogramming do provide a ForeignFunctionInterface which can be used to AlternateHardAndSoftLayers, thus providing an "escape hatch").

In some languages (many of them typeless/single-type languages where the only type provided is a machine word), virtually all programming is PointerMetaprogramming. One classic example is C's predecessor BeeLanguage. Another is ForthLanguage (though that comment ought to be taken with a grain of salt, as there really isn't a single language called "Forth", and some Forth dialects do impose types).

See also PointerCastPolymorphism and some related discussion on FirstClass.

See also ThreeStarProgramming.

CategoryPolymorphism CategoryMetaprogramming

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