Great introduction to c metaprogramming by simon tatham can be found here. The problems were solved by the traits template idiom see 3. 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. Write high performance code by eliminating virtual member function calls. Literally, each of us may be our programs, nothing more, nothing less.
Sep 09, 20 templates can be used to perform compiletime calculations on data that is known, of course, at compile time. The use of templates can be thought of as compiletime execution. The complete guide since it is also the definitive reference for templates in general. This allows computations to be performed once at compile time rather than at each run time. The two newer standards are not used in the code so that the examples can be rich, illustrate the. Recently, however, ive faced a problem that could not be solved by the means outlined in the article. Perhaps surprisingly, in view of the fact that templates are functional programs, func. None of us can escape our own nature as programmable entities. Metaprogramming or more specifically, template metaprogramming is the practice of using templates to create constants, functions, or data structures at compiletime. This section contains examples about template metafunctions. Despite the extremely baroque nature of template metaprogramming, templates are used in fascinating ways that extend beyond the wildest dreams of the language designers 1. This recursion will end if the fully specialised class template factorial kicks in in line 3. Concepts, tools, and techniques from boost and beyond pdf, epub, docx and torrent then this site is not for you.
The reason is that tm can generate arbitrary code from the templates, but cannot modify the nontemplate code. 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. The basics template metaprogramming tmp arose by accident. Im going to start with an example from the ruby on rails framework. Template specialization a version of a template to use when a specific pattern of arguments are supplied. Variablefunctions names i usually prefer to have only one of two possible public operations defined in a tmp class. That doesnt work if the language doesnt support metaprogramming well.
Weve had the idea of writing about template metaprogramming for. The compiler must then decide which ones to use the rules of these decisions and how the compiler does this can get very complicated and lead to issues. Things like template, which look really weird but behave in an even more bizarre way. Technically metaprogramming is code that writes code. Metaprogramming with templates yes, the code checks whether the number is a prime number template struct isprime2 static const int resisprime2 metaprogramming 7 was published in 1995. The chapter presents further examples for this usage as well. Overloading function templates like ordinary functions, function templates can also be overloaded.
A metaprogram is a program that generates or manipulates program code. For ease of use and to avoid this for simple templates we can use a header and an inline function. Metaprogramming in c is the art of creating new language constructs, typically using macros. This post starts a series of articles following the contrived and tortuous path down insanity lane. And inspiring introduction to template metaprogramming.
Lets cover variable templates first, because theyre a lot like class templates. 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 is a programming technique in which computer programs have the ability to treat other programs as their data. Concepts, tools, and techniques from boost and beyond pdf,, download ebookee alternative successful tips for a improve ebook reading experience. During this instantiation, factorial value will be instantiated. Download pdf c template metaprogramming book full free. Most people insist on trying to metaprogram from inside their favorite language.
The if template was the rst control structure in a generic form 3 and the remaining control structures were published in 4. Before going into the description of our obfuscator, it is necessary to give some basis of the mechanism involved. 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. 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. In general, macros are frowned upon in this role and templates are preferred, although they are not as generic. Since you dont have mutable variables available when youre programming with templates, its impossible to iterate over a sequence of values.
Template metaprogramming is much more fun than mere generic classes. Not everyone needs to know or needs to use metaprogramming techniques to be a good programmer, and it might look like a. A way around this is to do metaprogramming from outside the language, using program transformation tools. Full specialization used when all arguments are specified. Template metaprogramming is challenging enough without trying to generalize the class to support multiple operations. Written by industry leaders, the book begins with the simplest of topics function templates and builds its way through the most daunting of topics to master partial specialization and metaprogramming. Need help mixing computed goto and loop unrolling via template metaprogramming. So, using templates, we can write programs that do computation at compile time, such programs are called template metaprograms. Programming and metaprogramming in the human biocomputer all human beings, all persons who reach adulthood in the world today are programmed biocomputers. This technique is called template metaprogramming tmp.
It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself while running. In some cases, this can be used to optimize the eventual runtime of a program. There have been some articles dealing with template metaprogramming before over here. Partial specialization used when arguments have a particular structure. Pdf c template metaprogramming download full pdf book. In many ways, that collection of templates was the precursor to the boost metaprogramming library mpl. Originally, templates were designed to enable generic programming and provide type safety. Metaprogramming allows programs to create methods on the fly instead of having to define them in the program itself.
An introduction to metaprogramming for scientific computing dr conrad sanderson senior research scientist version 1. Metafunction aka type traits is a template metaprogramming technique for type introspection, type manipulation and type computation. A complete mpl reference manual, in html and pdf form. The call factorial value in line 1 causes the instantiation of the primary or general template in line 2. Template metaprogramming often makes use of compiletime computations, whether via templates or constexpr functions. C template metaprogramming available for download and read online in other formats. The output of these templates include compiletime constants, data structures, and complete functions. Template metaprogramming 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. The rst article on template metaprogramming 7 was published in 1995. Mos 4465a is an advanced financial ac modern advanced accounting in canada, 8th edition, mcgraw. However, before you get visions in your mind of robots writing code to take over the world, understand that its actually much less intense.995 526 634 980 719 1507 40 1246 122 183 880 310 1477 1217 1054 1562 1173 1540 696 1251 577 1060 383 1584 136 1089 555 1400 612 994 1023 1277 40 525 1242 1342