Basics: Templates – Part 2 Bob Steagall CppCon 2021CppCon 2021 – Back to Basics: Templates – Part 2 Copyright © 2021 Bob Steagall Recap: Templates • C++ supports generic programming with templates • A kinds of templates • Function templates • Class templates • Member function templates • Alias template • Variable templates • Lambda templates 2CppCon 2021 – Back to Basics: Templates – Part 2 Copyright inclusion preprocessing directives (#ifdef) • And all macros expanded 3CppCon 2021 – Back to Basics: Templates – Part 2 Copyright © 2021 Bob Steagall Recap: Declarations and Definitions • A name is an identifier

Back to Basics: Templates – Part 1 Bob Steagall CppCon 2021CppCon 2021 – Back to Basics: Templates – Part 1 Copyright © 2021 Bob Steagall Overview • Rationale • Template fundamentals • Template categories categories in detail 2CppCon 2021 – Back to Basics: Templates – Part 1 Copyright © 2021 Bob Steagall Goals and References • Goals • Cover major features • Explain some important terminology and concepts concepts • Point to next steps • Recommended references • C++ Templates The Complete Guide, Second Edition David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor – Addison-Wesley 2018 • Effective Modern

Info @Andreas__Fertig B2B: C++ Templates Part 1 fertig adjective /ˈfɛrtɪç/ finished ready complete completed Andreas Fertig v1.0 B2B: C++ Templates 2 B2B: C++ Templates ­ Part 1 © 2020 Andreas Fertig flexi­ bility. Andreas Fertig v1.0 B2B: C++ Templates 3 Templates ■ Templates are a kind of pattern for the compiler. ■ We can instantiate templates with different types or values. ■ Each instantiation ment. ■ Templates reduce a lot of writers’ work. We do not have to implement functions multiple times just because it’s a slightly different type. ■ There are different types of templates: ■ Function­templates

Fertig https://AndreasFertig.Info post@AndreasFertig.Info @Andreas__Fertig B2B: C++ Templates Part 2 Variadic templates: Parameter pack ■ Syntax: A typename|class... Ts generates a type template pa­ rameter B2B: C++ Templates 2 B2B: C++ Templates ­ Part 2 © 2020 Andreas Fertig https://AndreasFertig.Info post@AndreasFertig.Info 1Variadic templates ■ With C++11, there are variadic templates: ■ Variadic Variadic templates are templates that take any number of parameters. ■ Already known by variadic macros or variadic functions. 1 A Helper functions to convert everything into a std::string 2 auto Normalize(const

Sample() // Retrieve an RSS feed and print it. { Uri uri(L""); SyndicationClient client; SyndicationFeed feed = co_await client.RetrieveFeedAsync(uri); for (auto&& item : feed.Items()) { hstring engineer ▪ The final throughput gain was had by finding that partial specializations of class templates dominated the compile time ▪ Let’s delay them... 46 (C) Dos Reis & DaCamara; CppCon 2021IDE Experience

public: virtual core::Expected:> add(const window::Uri& windowUri) = 0; }; ./ ... core::Expected:> WindowLayoutStack::add(const window::Uri& windowUri) { return loadWindow(windowUri, m_windowLoader) yout> m_windowLayout; }; 40Example: window layout wrapper void WindowLayout::add(const window::Uri& windowUri) { m_windowLayout:>add(windowUri).or_else(&printError); } 41What did we achieve? std::shared_ptr loadWindow( const window::Uri &windowUri, const window::Loader &loader); ./ ... bool WindowLayoutStack::add(const window::Uri& windowUri) { if (auto window = loadWindow(windowUri

math.  2MOTIVATION • Templates are a powerful tool for C++ programmers. • Each C++ version has evolved templates, allowing better usage. • We’ll see the value of adding templates to your code. 3MOTIVATION use of templates 4 • We’ll see how C++20 creates a paradigm shift in the way we use metaprogramming. And I don’t blame them…• Part 0: (Prologue) What are templates? • Part I: Adding templates to existing beyond…) • Part V: Advanced methods for controlling compile time logic OUTLINE 5PART 0: WHAT ARE TEMPLATES? 6• A template allows creating a class or a function template class TemplatedClass

different, unrelated types Static polymorphism9 David Olsen – Generic Programming CppCon 2024 C++ Templates Same code works on different, unrelated types Static polymorphism10 David Olsen – Generic Programming correctness of the definition46 David Olsen – Generic Programming CppCon 2024 Substitution Class templates Substitution without instantiation in two contexts Incomplete type is sufficient Class template template arguments are checked47 David Olsen – Generic Programming CppCon 2024 Substitution Class templates Substitution without instantiation in two contexts Incomplete type is sufficient Class template

symbol with no templates 6 . 12SAVE LIBRARY/BINARY SAVE LIBRARY/BINARY MAIN.CPP MAIN.CPP #include // std::stoi void dispatch(int); // _Z3dispatchi - Mangled symbol with no templates int main(int #include // std::stoi void dispatch(int); // _Z3dispatchi - Mangled symbol with no templates int main(int argc, const char** argv) { dispatch(std::stoi(argv[1])); } $LLC -filetype=obj #include // std::stoi void dispatch(int); // _Z3dispatchi - Mangled symbol with no templates int main(int argc, const char** argv) { dispatch(std::stoi(argv[1])); } $LLC -filetype=obj

. . . . . . . . . . 26 2.5 Templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3 CONTENTS CONTENTS Extern templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Type alias templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Variadic templates . . . . . . . . . . . . . . . . . . . . . . t) { return t + 0.001; } int main() { std::cout << print_type_info(5) << std::endl; 25 2.5 Templates CHAPTER 02: LANGUAGE USABILITY ENHANCEMENTS std::cout << print_type_info(3.14) << std::endl; }