This post starts a series of articles following the contrived and tortuous path down insanity lane. This makes it possible to create a template which calculates a value at return time, a value which can then be used as a constant in the rest of the program. In general, macros are frowned upon in this role and templates are preferred, although they are not as generic. Included as a sample is a small class that does generic crc cyclic redundancy codes a set of simple hash algorithms calculations. Trait classes are a familiar example of a simple form of template metaprogramming. For example, you can convert simple expressions to more complicated expressions, or examine code before it runs and change it so that it runs faster. A traditional program is mainly code that manipulates a data structure and produces output. Well, it was the best collective term we could come up with for the set of things that are more about process than they are about writing code or working more efficiently.
It allows even inexperienced programmers to perform compiletime computations without doing any tmp on the surface. An introduction to template metaprogramming barney dellar. Metaprogramming with metaclasses in python geeksforgeeks. The output of these templates include compiletime constants, data structures, and complete functions. Metaprogramming allows programs to create methods on the fly instead of having to define them in the program itself. Recently, however, ive faced a problem that could not be solved by the means outlined in the article. An example of this is an sqrt function that takes an integer i. Introducing juliametaprogramming wikibooks, open books for. Template metaprogramming is in fact turingcomplete, meaning that any computation expressible by a computer program can be computed, in some form, by a template metaprogram. When this is the case, you can use metaclass programming to modify the way that some of. Therefore, i call this projecttechnique template metaprogramming programming. This allows computations to be performed once at compile time rather than at each run time.
So in above example, unlike c or java where int, char, float are primary data types, in python they are object of int class or str class. For example, code for resetting this tensor of vectors should be. That s why on the surface it might look arcane, but after you are. The first index can be variable, yet the second must be a constant. A light bulb went off in my head as soon as i read this canonical metaprogramming example.
In order to explain metaprogramming, let me explain a few basic concepts first. Sep 09, 20 what weve done now is program a little function or subroutine that is evaluated compiletime, using tmp. Though the syntax of template metaprogramming is usually very different from the programming language it is used with, it has practical uses. Metaprogramming the missing semester of your cs education. However, with julias metaprogramming facilities, you can access the code after its been parsed but before its evaluated. An introduction to metaprogramming for scientific computing dr conrad sanderson senior research scientist version 1. Im going to start with an example from the ruby on rails framework. An introduction to template metaprogramming barney dellar software team lead toshiba medical visualisation systems. Great introduction to c metaprogramming by simon tatham can be found here. Monkey patching is an object oriented programming technique that allows developers to.
Metaprogramming is a programming technique in which computer programs have the ability to treat other programs as their data. Metaprogramming is the act of writing metaprograms. Jonathan cohen nvidia research gtc, san jose convention center, ca sept. In this lecture, we will look at systems for building and testing your code, and for managing dependencies. For example, to make a test to see if a class has a public method with the signature void printint you would say. Pdf c template metaprogramming download ebook for free.
In a small summary report written for the national institute of mental health, entitled programming and metaprogramming in the human biocomputer 19661967, lilly lends his unique insight after five years of research combining lsd25 and sensory deprivation to alter behavioral and cognitive patterns in. It allows even inexperienced programmers to perform compile. In a small summary report written for the national institute of mental health, entitled programming and metaprogramming in the human biocomputer 19661967, lilly lends his unique insight after five years of research combining lsd25 and sensory deprivation to alter behavioral and cognitive patterns in the mind. While i consider myself falling rather in the camp of the aficionados, ive met a lot more people that dont have a strong interest for it, or that even find it downright disgusting, than tmp enthusiasts. In nutshell we can say metaprogramming is the code which manipulates code. Template metaprogramming tmp is a metaprogramming technique in which templates are used by a compiler to generate temporary source code, which is merged by the compiler with the rest of the source code and then compiled.
Programming and metaprogramming in the human biocomputer. Because we are generating code at compile time, we cannot update state, so we have to. At first word metaprogramming seems very funky and alien thing but if you have ever worked with decorators or metaclasses, your were doing metaprogramming there. This is different from the web application model where. This article describes a technique for using the c preprocessor to implement a form of metaprogramming in c, allowing a programmer to define custom looping and control constructions which behave syntactically like c s own for, while and if. So we can make a new type by creating a class of that type.
Copyright c 20, decorators with args 47 from functools import wraps def debugprefix. In some cases, this allows programmers to minimize the number of lines of code to express a solution hence reducing development time. I have very simple program that uses tmp,it calculates the square of a number, but it doesnt seem to. Things like template, which look really weird but behave in an even more bizarre way. Each language subclass described specific processing traits for that language. Download c template metaprogramming ebook free in pdf and epub format. Metaprogramming is frowned on in python and considered unpythonic. Template metaprogramming is generally not used in practical programs, it is an interesting conecpt though.
It seems really cool, make the compiler do most of the work. Static metaprogramming 1 static time integer 4 mytype 8 compiler 20 base level metaprogram and metaobjects exist only at compile time. The use of templates can be thought of as compiletime execution. Yes, its a weird name, but its a powerful and dangerous tool. Template metaprogramming is generally not used in practical programs, it. Starting off the list for examples of metaprogramming is monkey patching. The only widely known example of metaprogramming in python was an implementation of a goto and comefrom keyword done as an aprilfools joke. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself while running. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Metaprogramming in c is the art of creating new language constructs, typically using macros. Being late to the metaprogramming party, i make no claim of having invented the techniques in this article. Efficient algorithms for membership testing, random access, and retrieval by key. In this article we are going to discuss about metaclasses, why and when we should use them and what are the. Another more recent library that shows it can be done in python is macropy.
The main reason i chose crc for this article is that the crc algorithms usually use a lookup table based on a. In fact many template implementations implement flow control only through recursion, as seen in the example below. What weve done now is program a little function or subroutine that is evaluated compiletime, using tmp. A possible stub for some future answers, so that this larger one could be eventually rewritten andor split into more focused and narrow ones, as the interest towards some particular forms of metaprogramming in mathematica is being developed in our community. There have been some articles dealing with template metaprogramming before over here. The default metaclass is called type and in the vast majority of cases it does the right thing. Metaprogramming is the writing of computer programs that write or manipulate other programs or themselves as their data, or that do part of the work at compile time that would otherwise be done at runtime.