templates.md

Templates

Table of contents

• Introduction and overview
  • Applications
• Template arguments
  • Argument deduction
    • Class template argument deduction (CTAD)
    • Deduction guides
• Concepts
  • Standard concepts
  • Applications
• Function templates
  • Friend function templates
• Parsing and compilation
  • Optimization
    • extern template
  • Two-phase lookup
    • Keywords template and typename as disambiguators
• SFINAE
  • Detection idiom
• Specialization
• Explicit instantiation
• Tuples
• Type lists
• Type traits
• Variadic templates
  • Fold expressions

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Introduction and overview

🔗

• S.Golodetz. Functional programming using C++ templates (Part I) – Overload 81 (2007)
• S.Golodetz. Functional programming using C++ templates (Part II) – Overload 82 (2007)

❔

• Templates – C++ FAQ

🎥

• J.Hagins. Template metaprogramming: Practical application – CppCon (2021)
• H.Matthews. The C++ type system is your friend – ACCU (2017)
• W.E.Brown. Modern template metaprogramming: A compendium. Part I, Part II – CppCon (2014)
• A.Modell. C++ advanced topics in templates – Tech Talk (2014)
• M.Caisse. Introduction to modern C++ techniques. Part I, Part II – C++Now (2012)

📄

• B.Stroustrup. Parameterized types for C++ – Computing System 2, 55 (1989)

📖

• D.Vandevoorde, N.M.Josuttis, D.Gregor. C++ templates: The complete guide – Addison-Wesley (2017)
• A.Alexandrescu. Modern C++ design: Generic programming and design patterns applied – Addison-Wesley (2001)

Applications

🎥

• J.Gopel. Using modern C++ to eliminate virtual functions – CppCon (2022)

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Template arguments

🔗

• J.Müller. Tricks with default template arguments (2020)

Argument deduction

❔

• What is a nondeduced context? – Stack Overflow

🎥

• S.Meyers. Type deduction and why you care – CppCon (2014)

⚓

• Template argument deduction – C++ reference

Class template argument deduction (CTAD)

🔗

• A.O’Dwyer. Beware CTAD on reverse_iterator (2022)
• A.O’Dwyer. Thoughts on -Wctad-maybe-unsupported (2022)
• R.Orr. CTAD – What is this new acronym all about? – Overload 143 (2019)

❔

• Is std::make_move_iterator redundant since C++17’s class template argument deduction? – Stack Overflow

🎥

• M.Clow. Class template argument deduction: History, how to ise it, and how to enable it for your classes – CppCon (2022)
• T.Doumler. Class template argument deduction in C++17 – CppCon (2018)
• T.Doumler. Class template argument deduction in C++17 – ACCU (2018)
• S.T.Lavavej. Class template argument deduction for everyone – CppCon (2018)
• Z.Yuan. Class template argument deduction: A new abstraction – CppCon (2017)

⚓

• M.Spertus, F.Vali, R.Smith. Template argument deduction for class templates – WG21/P0091

Deduction guides

❔

• What are template deduction guides and when should we use them? – Stack Overflow

⚓

• Deduction for class templates – C++ reference

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Concepts

See also Concepts – The standard library and proposals.

🔗

• A.Krzemieński. Concepts – case studies (2021)
• A.Krzemieński. Semantic requirements in concepts (2020)
• A.Sutton. Defining concepts – Overload 131 (2016)
• A.Sutton. Introducing concepts – Overload 129 (2015)

❔

• How will concepts lite interact with universal references? – Stack Overflow
• Why does same_as concept check type equality twice? – Stack Overflow

🎥

• J.Garland. Using concepts: C++ design in a concept world. Part I, Part II – C++Now (2021)
• R.Barkan. Semantic sugar: Tips for effective template library APIs – C++Now (2021)
• H.Matthews. C++ concepts for developers – NDC (2019)
• R.Grimm. Concepts in C++20: Revolution or evolution – CppCon (2019)
• B.Stroustrup. Concepts: The future of generic programming (the future is here) – CppCon (2018)

⚓

• W.E.Brown. enable_if vs.requires: A case study – WG21/P0552

Standard concepts

❔

• Why is the std::derived_from concept implemented with an additional convertibility test that adds cv-qualifiers? – Stack Overflow

Applications

🔗

• A.Fertig. C++20 concepts applied – Safe bitmasks using scoped enums (2024)

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Function templates

🔗

• H.Sutter. Why not specialize function templates?

❔

• Necessity of forward-declaring template functions – Stack Overflow

🎥

• B.Saks. Back to basics: Function call resolution in C++ – CppCon (2024)
• W.E.Brown. C++ function templates: How do they really work? – C++ on Sea (2019)
• W.E.Brown. C++ function templates: How do they really work? – CppCon (2018)

Friend function templates

❔

• Why do I get linker errors when I use template friends? – C++ FAQ
• Correct syntax for friend template function – Stack Overflow

🎥

• D.Saks. Making new friends – CppCon (2018)

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Parsing and compilation

🔗

• C++ keyword of the day: export (2008)

❔

• Why do templates use the angle bracket syntax? – Stack Overflow
• How do compilers eliminate the need to write white spaces between closing angle brackets, when using template classes since C++ 11 standard? – Quora

⚓

• D.Vandevoorde. Right angle brackets – WG21/N1757

Optimization

🔗

• C.DaCamara. Improving the state of debug performance in C++ (2022)
• A.O’Dwyer. Benchmarking Clang’s -fbuiltin-std-forward (2022)
• D.Pallastrelli. Reduce compilation times with extern template (2019)
• L.Dionne. Efficient parameter pack indexing (2015)
• A.Bergé. True story: Efficient packing (2015)

🎥

• J.Brown. Reducing template compilation overhead, using C++11, 14, 17, and 20 – CppCon (2019)

extern template

❔

• Using extern template with third-party header-only library – Stack Overflow

Two-phase lookup

Names are resolved in two steps: first, non-dependent names are resolved at the time of template definition and, second, dependent names are resolved at the time of template instantiation.

🔗

• T.Gani et al. Two-phase name lookup support comes to MSVC – Microsoft C++ team blog (2017)
• Two-phase lookup in C++ templates (2014)
• E.Bendersky. Dependent name lookup for C++ templates (2012)

❔

• Why do I have to access template base class members through the this pointer? – Stack Overflow

⚓

• J.Wilkinson, J.Dehnert, M.Austern. A proposed new template compilation model – WG21/N0906

Keywords template and typename as disambiguators

struct S { template<typename T> using type = T; };
template<class T> void foo() { typename T::template type<int> x; }

foo<S>();

🔗

• H.Sutter. GotW #35: Typename

❔

• Why don’t I need to specify typename before a dependent type in C++20? – Stack Overflow
• Where and why do I have to put the template and typename keywords? – Stack Overflow

🎥

• A.Stepanov. Efficient programming with components (part of Lec. 12) – A9 (2013)

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SFINAE

"Substitution Failure Is Not An Error" – when substituting the explicitly specified or deduced type for the template parameter fails, the specialization is discarded from the overload set instead of causing a compile error.

🔗

• Substitution failure is not an error – Wikipedia

❔

• What exactly is the “immediate context” mentioned in the C++11 Standard for which SFINAE applies? – Stack Overflow
• What is “Expression SFINAE”? – Stack Overflow
• How does std::void_t work – Stack Overflow
• SFINAE and partial class template specializations – Stack Overflow
• SFINAE examples? – Stack Overflow

⚓

• SFINAE – C++ reference

Detection idiom

• P.Barber. Unit testing compilation failure – Overload 108 (2012)

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Specialization

🔗

• A.O’Dwyer. Don’t reopen namespace std (2021)
• O.Wigley. Alternatives for partial template function specialisation – Overload 50 (2002)

❔

• Partial specialization of template class copy constructor – Stack Overflow

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Explicit instantiation

• A.O’Dwyer. Don’t explicitly instantiate std templates (2021)

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Tuples

🔗

• N.Deppe. Template metaprogramming. Part 3: Tuple iteration with recursion (2017)
• N.Deppe. Template metaprogramming. Part 4: Recursion free tuple iteration (2017)

🎥

• J.Brown. Reducing template compilation overhead, using C++11, 14, 17, and 20 – CppCon (2019)
• A.Modell. C++ advanced topics in templates – Tech Talk (2014)

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Type lists

🔗

• N.Deppe. Template metaprogramming. Part 2: Typelist (2017)
• J.Galowicz. Type lists (2016)
• J.Galowicz. Type list compile time performance (2016)
• J.Galowicz. Transformations between user input/output and type lists (2016)

📖

• Ch. 3: Typelists – A.Alexandrescu. Modern C++ design: Generic programming and design patterns applied (2001)

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Type traits

See also Type traits – The standard library and Boost.

🔗

• J.Müller. Trivially copyable does not mean trivially copy constructible (2021)
• J.Müller. Technique: Immediately-invoked function expression for metaprogramming (2020)
• N.Deppe. Template metaprogramming. Part 1 (2017)
• T.Frogley. An introduction to C++ traits – ACCU (2001)
• J.Maddock, S.Cleary. C++ type traits (mirror) – Dr. Dobb’s Journal (2000)

❔

• What are the 15 classifications of types in C++? – Stack Overflow

🎥

• J.Hagins. Template Metaprogramming: Type Traits. Part 1, Part 2 – CppCon (2020)
• A.O’Dwyer. The best type traits that C++ doesn’t have – C++Now (2018)
• H.Matthews. The C++ type system is your friend – ACCU (2017)

⚓

• C++ named requirements: UnaryTypeTrait – C++ reference
• C++ named requirements: BinaryTypeTrait – C++ reference
• C++ named requirements: TransformationTrait – C++ reference

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Variadic templates

🔗

• E.Bendersky. Variadic templates in C++ (2014)

❔

• Variadic template pack expansion – Stack Overflow

🎥

• M.Dominiak. “Variadic expansion in examples – CppCon (2016)

⚓

• B.Seymour, S.T.Lavavej. Searching for types in parameter packs – WG21/N4115

Fold expressions

🔗

• J.Müller. Nifty fold expression tricks (2020)
• A.O’Dwyer. Folding over operator= (2020)

⚓

• Fold expression – C++ reference