I was motivated to write this after i read eric nieblers thoughtprovoking tiny metaprogramming library article. There have been some articles dealing with template metaprogramming before over here. Template metaprogramming is generally not used in practical programs, it is an interesting conecpt though. So, ill recommend the new edition of my book mentioned by the other answers.
Things like template, which look really weird but behave in an even more bizarre way. For instance, consider compiletime regex matcher using constexpr. Static polymorphism is a high performance alternative to dynamic polymorphism, inheritance, and virtual methods since all called functions are resolved at compiletime. This recursion will end if the fully specialised class template factorial kicks in in line 3. Recently, however, ive faced a problem that could not be solved by the means outlined in the article. Being late to the metaprogramming party, i make no claim of having invented the techniques in this article. After 15 chapters of template metaprogramming you should have learned why staying away from them is a good idea, but if you have been following this series then you should know now when and why they could be useful. Allows you to use typename instead of class when declaring a template template parameter. Lets cover variable templates first, because theyre a lot like class templates.
The compiler acts as an interpreter or a virtual computer that emits the instructions that make up the final program. Until that time, you can read about two of the new techniques here. Efficient algorithms for membership testing, random access, and retrieval by key. Matching of template template arguments excludes compatible templates. The use of templates can be thought of as compiletime polymorphism. A function template behaves like a function except that the template can have arguments of many different types see example. This allows us to write a function that takes a variable number of parameters in a typesafe manner. A metaprogram is a program that generates or manipulates program code. Here we will put greater emphasis to the relation of templates to type parametrization than their compiletime computation aspect, sometimes called metaprogramming. Reading these articles before proceeding with this documentation is highly recommended.
Great introduction to c metaprogramming by simon tatham can be found here. Pdf c template metaprogramming download full pdf book. Normal type parameters can use them interchangeably, but template template parameters were restricted to class. W e ve had the idea of writing about template metaprogramming for. If you are into functional programming several other options are also available. Caveat i decided to do this talk after getting thoroughly lost.
Before going into the description of our obfuscator, it is necessary to give some basis of the mechanism involved. The call factorial value in line 1 causes the instantiation of the primary or general template in line 2. The if template was the rst control structure in a generic form 3 and the remaining control structures were published in 4. Even if the template mechanism generates code under the hood and thats a type of metaprogramming, you know perfectly what the community knows as tmp. A macro is a piece of code that executes at compile time and either performs textual manipulation of code tobe compiled e. Template metaprograms can generate useful code when interpreted by the compiler, such as a massively inlined algorithm that is, an implementation of an algorithm which works for a specific input size, and has its loops unrolled. Template function can be executed at runtime and constexpr functions can be templated. Template metaprogramming is something that originated by accident, as a side effect of the original template mechanism, which was intended as a way to allow writing small generic functions. The chapter presents further examples for this usage as well. You can also consider it a short introduction into basic concepts of metaprogramming in general. This will surely cover all the interesting aspects of the new metaprogramming tools. It can, for the most part, be considered to be programming with types in that, largely, the.
Template metaprogramming is generally not used in practical programs, it. During this instantiation, factorial value will be instantiated. With variadic templates, parameter packs and template aliases. This allows computations to be performed once at compile time rather than at each run time. 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.
Jun 26, 2017 allow typename in a template template parameters. The range of userdefined types that can be cleanly and safely expressed has grown with the addition of features such as initializerlists, uniform initialization, template aliases, rvalue references, defaulted and deleted functions, and variadic templates. An introduction to metaprogramming for scientific computing dr conrad sanderson senior research scientist version 1. In addition to nico josuttis and myself, doug gregor clang pioneer, swift co. Jul 12, 2017 outright rejection is probably more accurate. Originally, templates were designed to enable generic programming and provide type safety. A complete mpl reference manual, in html and pdf form. 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. Even though this language feature now exists however, it may not be prudent to use it in all cases where youd do something like this. Metaprogramming in c is the art of creating new language constructs, typically using macros. 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. The rst article on template metaprogramming 7 was published in 1995. It means that a program can be designed to read, generate, analyze or transform other programs, and even modify itself while running. Lipari scuola superiore santanna template metaprogramming april 6, 2011 11 41 integral template parameters the parameters of a template can be constant numbers instead of.
This post starts a series of articles following the contrived and tortuous path down insanity lane. An introduction to template metaprogramming barney dellar software team lead. In mathematics, the factorial of a nonnegative integer n, denoted by n. And inspiring introduction to template metaprogramming.
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