©2024 by josuttis.com 1 C++ Nicolai M. Josuttis josuttis.com @NicoJosuttis C++ Concepts September 18, 2024 14:00 - 15:00 MDT ©2024 by josuttis.com 2 C++ Nicolai M. Josuttis • Independent consultant Architect – Technical Manager – SOA – X and OSF/Motif Nico Josuttis C++ Concepts @cppcon 2024-09-18 1©2024 by josuttis.com 3 C++ Concepts, Constraints, and Requirements C++20 ©2024 by josuttis.com 4 C++ add(coll1, 42); // OK add(coll2, 42); // ERROR: no push_back() C++98 Nico Josuttis C++ Concepts @cppcon 2024-09-18 2©2024 by josuttis.com 5 C++ Overloading Function Templates template

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in a class - Interfaces - Pimpl idiom - Wrapper classes as a view, wrapping the original - C++20 Concepts (?) 56 Hiding your Implementation Details, Amir Kirsh @ CppCon, 2024 Passing args, exposing only Implementation Details, Amir Kirsh @ CppCon, 2024 A Meander: ConceptsWhat’s a Concept? 60 A Meander: Concepts ● A constraint on template arguments ● Evaluated to a boolean value, at compile time ● May be overload resolution A much more elegant and simple substitute for SFINAEFirst Example 61 A Meander: Concepts We want to overload two generic functions: // for types that we can iterate over template

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sion.hpp> CppCon 2020 | A Physical Units Library For the Next C++ Generic code: Boost.Units + Concepts (godbolt.org/z/erfbzr) 24#include template; CppCon 2020 | A Physical Units Library For the Next C++ Generic code: Boost.Units + Concepts (godbolt.org/z/erfbzr) 24#include templateConcepts (godbolt.org/z/erfbzr) 24template concept Length = units::traits::is_length_unit::value;

Generic Programming” paper, we see that regular types naturally appear as necessary foundational concepts in programming. Why do we need to bother with such taxonomies? Because STL assumes such properties behavior for the caller. This talk will explore the relation between Regular types (plus other concepts) and STL constructs, with examples, common pitfalls and guidance.2023 Victor Ciura | @ciura_victor talking about this ? We shall see that Regular types naturally appear as necessary foundational concepts in programming and try to investigate how these requirements fit in the ever expanding C++ standard

}Outline - Background (Ranges, Parallelism, Distributed Data Structures) - Distributed Ranges (Concepts) - Implementation (Algorithms and views) - Complex Data Structures (Dense and sparse learnedOutline - Background (Ranges, Parallelism, Distributed Data Structures) - Distributed Ranges (Concepts) - Implementation (Algorithms and views) - Complex Data Structures (Dense and sparse T(0), std::plus()); }Standard C++ Parallelism - All depends on ranges library, iteration concepts - Extensible: execution policies allow parallel execution using namespace std; using namespace

Background: How and why to use matrix algebra for graphs? What are the important data structures and concepts? Prior work in the GraphBLAS community, C API Overview of our draft C++ API How might this interoperate Background: How and why to use matrix algebra for graphs? What are the important data structures and concepts? Prior work in the GraphBLAS community, C API Overview of our draft C++ API How might this interoperate Background: How and why to use matrix algebra for graphs? What are the important data structures and concepts? Prior work in the GraphBLAS community, C API Overview of our draft C++ API How might this interoperate

else { last = p; } } return value; } 28 . 1ITERATOR CATEGORIES (CONCEPTS) ITERATOR CATEGORIES (CONCEPTS) input_iterator output_iterator forward_iterator bidirectional_iterator random_access_iterator random_access_iterator contiguous_iterator C++17 iterator categories got a concepts specification in C++20. C++17 iterator categories got a concepts specification in C++20. All of these expose All of these expose Which concept(s) do they require? also informs complexity guarantees, maybe different for different concepts 30 . 1ITERATOR CONCEPT QUESTIONS ITERATOR CONCEPT QUESTIONS 1. Am I using any standard algorithms

Inverse: 𝑞−1 = 𝑞∗ 𝑞 2 = 𝑞∗ 𝑞∙𝑞 • Division: 𝑎 𝑏 = 𝑎𝑏1 = 𝑎𝑏∗ 𝑏∙𝑏Quaternion Concepts in Mathematics vs. C++ 20 • Mathematically, a quaternion is defined by its data and operations its data • The common implementation of operations rely only upon the concepts • Optimized implementations conform to the concepts and common implementationsC++ Quaternion Concept template std::same_as; { q.z() } -> std::same_as; };Supporting Concepts Arithmetic MutuallyArithmetic template concept Arithmetic = std::is_arithmetic_v;

CONDITIONS AT COMPILE TIME USING C++20 25• C++20 created a paradigm shift in metaprogramming. • Concepts and constraints allow the user to introduce a new ‘type category’ (vs. type) to the compiler. PART is_pointer_interconvertible_with_class is_corresponding_member is_constant_evaluated();Concepts: • Concepts are a way for the developer to define restrictions on the “type category”. template ; int main() { cout << "Trivial: " << trivial << '\n'; // Trivial: 1 } Concepts: • Concepts can be used to identify whether a type belongs to the “type category” template

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does nothing // Default case 6 . 13QUESTIONS? QUESTIONS? 6 . 14JIT & CONCEPTS JIT & CONCEPTS 6 . 15JIT & CONCEPTS JIT & CONCEPTS template concept readable_io = requires(TIO& io, std::byte* size) { { io.read(buffer, size) } -> std::same_as; }; 6 . 15JIT & CONCEPTS JIT & CONCEPTS template concept readable_io = requires(TIO& io, std::byte* buffer, std::size_t my_readable_io { auto read(std::byte* buffer, std::size_t size) -> std::size_t; }; 6 . 15JIT & CONCEPTS JIT & CONCEPTS template concept readable_io = requires(TIO& io, std::byte* buffer, std::size_t