You can use templates to define functions as well as classes, let us see how they work. This document was created by an unregistered chmmagic. 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. An introduction to metaprogramming for scientific computing dr conrad sanderson senior research scientist version 1. Consider a variant of stdfind that takes a sequence instead of a pair of iterators. This allows computations to be performed once at compile time rather than at each run time. I have very simple program that uses tmp,it calculates the square of a number, but it doesnt seem to. And inspiring introduction to template metaprogramming. These function templates can use these parameters as if they were any other regular type. The output of these templates include compiletime constants, data structures, and.
Im not an expert in any kind of compile time computing methods but i know that template metaprogramming provides such a functionality. The if template was the rst control structure in a generic form 3 and the remaining control structures were published in 4. Things like template, which look really weird but behave in an even more bizarre way. It allows even inexperienced programmers to perform compiletime computations without doing any tmp on the surface. Therefore, i call this projecttechnique template metaprogramming programming.
Sep 09, 20 what weve done now is program a little function or subroutine that is evaluated compiletime, using tmp. Template metaprogramming is generally not used in practical programs, it. This technique is called template metaprogramming tmp. A metaprogram is a program that generates or manipulates program code. This post starts a series of articles following the contrived and tortuous path down insanity lane and into the mouth of the beast. When c was developed, maths libraries implemented functions.
Metaprogramming is a programming technique in which computer programs have the ability to treat other programs as their data. Function templates these correspond roughly to polymorphic data types and polymorphic functions in functional languages. In the array class, we can define a data type for it. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself while running. On the other hand it might result in code bloat and performance decrease. This could be done to improve your programs runtime performance in exchange for slower compile times or. The first portion of this book covers the basics of template metaprogramming fairly well, but what i wanted the rest of the book to cover were both advanced techniques and realworld applications. Generally, constexprbased solutions are simpler, and promise to get much easier with future versions of the language. This allows us to create a function template whose functionality can be adapted to more than one type or class without repeating the entire code for each type.
Templates can be used to perform compiletime calculations on data that is known, of course, at compile time. Note that the second parameter is an int, not a type. Templates function templates function templates are special functions that can operate with generic types. You are expected to understand basic template syntax and template specialisation, and we will build the rest as we go along.
To a rst approximation, you can think of template instantiation as substitution of the formal parameters by the actual arguments. Practical techniques for building better software, philip romanik and. Template parameters can be types int including enum, short, char, bool etc. With help from the excellent boost metaprogramming library, david and aleksey take tmp from the laboratory to the workplace with readable prose and smart examples, displaying that compiletime stl is as able as its runtime counterpart. The first metaprogram history is just on damn thing after another nicolas cage inspiring. Yes, its a weird name, but its a powerful and dangerous tool. Tutorial loosely based on content in python cookbook, 3rd ed. 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. C style arrays but, what if we want to return an array with 5 elements. A light bulb went off in my head as soon as i read this cano. Template metaprogramming is a generic programming technique that uses extremely early binding. We can all learn enough to use it in our daytoday coding. It seems really cool, make the compiler do most of the work. Heres a really nice tutorial from the boost documentation pages actually excerpted from a brilliant book, well worth reading.
Lets pick up one of the classes in the standard librarythe array class. 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. This document was created by an unregistered chmmagic, please. This post starts a series of articles following the contrived and tortuous path down insanity lane. Type category declared type or deduced type of an expression value category. Starting off the list for examples of metaprogramming is monkey patching. In this example the metaprogram is not executed until the class template is instantiated. The rst article on template metaprogramming 7 was published in 1995. The compiler acts as an interpreter or a virtual computer that emits the instructions that make up the final program. I was motivated to write this after i read eric nieblers thoughtprovoking tiny metaprogramming library article. In some cases, this can be used to optimize the eventual runtime of a program. It can be used for static configuration, adaptive programs, optimization and much more.
Weve had the idea of writing about template metaprogramming for. Template metaprogramming is a great technique when used correctly. A template parameter is a special kind of parameter that can be used to pass a type as argument. Hana libraries, and functional reactive programming with the rxcpp. With variadic templates, parameter packs and template aliases. Another advantage is that you can look at a template class and immediately see if it is a template metaprogram or an ordinary template class. Metaprogramming with templates yes, the code checks whether the number is a prime number template jun 10, 20 this feature is not available right now. Boost library documentation template metaprogramming. The output of these templates include compiletime constants, data structures, and complete functions. The two newer standards are not used in the code so that the examples can be rich, illustrate the point, and be run with confidence. Abrahams and gurtovoy have written something close to a classic. The general form of a template function definition is shown here. Template metaprogramming scuola superiore santanna.
Template metaprogramming is generally not used in practical programs, it is an interesting conecpt though. Jun 21, 2015 essentially, metaprogramming is writing code that writes code hence the meta part. Dobbs journal, june 03, 2005 if youre like me, youre excited by what people do with template metaprogramming tmp but are frustrated at the lack of clear guidance and powerful tools. Lets cover variable templates first, because theyre a lot like class templates. Check out the best recommended c plus plus tutorials, courses and books upvoted and submitted by c. Monkey patching is an object oriented programming technique that allows developers to. But if we look again at the manual approach, we can see a certain. The use of templates can be thought of as compiletime execution. Metaprogramming or more specifically, template metaprogramming is the practice of using templates to create constants, functions, or data structures at compiletime. Pdf c template metaprogramming download full pdf book. Concepts, tools, and techniques from boost and beyond pdf, epub, docx and torrent then this site is not for you. There wont be a large list of books, as the list of people with a lot of experience is limited.
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