![Overview of C++20 and a deeper look into modules
Contracts
int push(queue& q, int val)
[[ expects: !q.full() ]]
[[ ensures !q.empty() ]]
{
==.
[[assert: q.is_ok() ]]
==.
}
https://www.reddit.com/r/cpp/comments/cmk7ek/what_happened_to_c20_contracts/
7
Precondition
Postcondition
Assertion](https://image.slidesharecdn.com/overviewofc20andadeeperlookintomodules-200415205056/85/Overview-of-C-20-and-a-deeper-look-into-modules-7-320.jpg)
 { return person.age < 14; })
| transform([](const auto& person) { return person.name; })
| to_vector;
https://vector-of-bool.github.io/2019/10/21/rngs-static-ovr.html
10](https://image.slidesharecdn.com/overviewofc20andadeeperlookintomodules-200415205056/85/Overview-of-C-20-and-a-deeper-look-into-modules-10-320.jpg)
![Overview of C++20 and a deeper look into modules
Modules > Names
module-name:
[module-name-qualifier] identifier ;
module-name-qualifier:
identifier "." | module-name-qualifier identifier "." ;
=> speech | speech.english
12](https://image.slidesharecdn.com/overviewofc20andadeeperlookintomodules-200415205056/85/Overview-of-C-20-and-a-deeper-look-into-modules-12-320.jpg)
![Overview of C++20 and a deeper look into modules
Modules > Declaration
module-declaration:
["export"] "module" module-name [module-partition] [attribute-specifier-seq] ";" ;
module-partition:
":" module-name ;
=> export module example;
13](https://image.slidesharecdn.com/overviewofc20andadeeperlookintomodules-200415205056/85/Overview-of-C-20-and-a-deeper-look-into-modules-13-320.jpg)
Overview of C++20 and a deeper look into modules
- 1. Overview of C++20 and a deeper look into modules export module cpp20; export bool doModulesRock() { return true; }
- 2. Overview of C++20 and a deeper look into modules Speaker ● Marius Meisenzahl ● Co-founder of ○ located in Bochum ○ we build software from embedded to web ○ we offer training for ■ testing ■ software architecture ■ DevOps ■ ... 2 /meisenzahl /meisenzahl
- 3. Overview of C++20 and a deeper look into modules C++20 Core Language Library Concurrency Four The Big Five ● Three-way comparison operator ● Strings literals as template parameters ● constexpr virtual functions ● Redefinition of volatile ● Designated initializers ● Various lambda improvements ● New standard attributes ● consteval and constinit keyword ● std=:source_location ● Calendar and time-zone ● std=:span as a view on a contiguous array ● constexpr containers such as std=:string and std=:vector ● std=:format ● std=:atomic_ref<T> ● std=:atomic<std=:shared_ptr<T=> and std=:atomic<std=:weak_ptr<T=> ● Floating point atomics ● Waiting on atomics ● Semaphores, latches and barriers ● std=:jthread ● Concepts ● Contracts ● Coroutines ● Ranges ● Modules 3
- 4. Overview of C++20 and a deeper look into modules Core Language > std=:source_location ● Provides access to file name, line number, ... ● Modern alternative to preprocessor macros like =_FILE=_ and =_LINE=_ ● Prime candidate for custom logging functionality in combination with std=:format https://en.cppreference.com/w/cpp/utility/source_location 4
- 5. Overview of C++20 and a deeper look into modules Library > std=:format ● https://github.com/fmtlib/fmt is integrated into C++ ● Python like string formatting ● Define formatting rules for custom types fmt=:print("Hello, {}!", "world"); std=:string s = fmt=:format("I'd rather be {1} than {0}.", "right", "happy"); 5
- 6. Overview of C++20 and a deeper look into modules Concurrency > std=:jthread ● A new kind of std=:thread ● Can automatically join ● Can be interrupted ○ std=:interrupt_token https://www.modernescpp.com/index.php/a-new-thread-with-c-20-std-jthread 6
- 7. Overview of C++20 and a deeper look into modules Contracts int push(queue& q, int val) [[ expects: !q.full() ]] [[ ensures !q.empty() ]] { ==. [[assert: q.is_ok() ]] ==. } https://www.reddit.com/r/cpp/comments/cmk7ek/what_happened_to_c20_contracts/ 7 Precondition Postcondition Assertion
- 8. Overview of C++20 and a deeper look into modules Concepts ● Extension of templates ○ specify which semantic categories are allowed ● Templates can be used more expressive ● Check types during compile time ○ “is sortable”, “is equality comparable”, … https://www.modernescpp.com/index.php/c-20-concepts-the-details 8
- 9. Overview of C++20 and a deeper look into modules Coroutines ● Asynchronous programming ○ cooperative multitasking, event loops, ... ○ new keywords co_await and co_yield ==. size_t n = co_await socket.async_read_some(buffer(data)); co_await async_write(socket, buffer(data, n)); ==. https://en.cppreference.com/w/cpp/language/coroutines 9
- 10. Overview of C++20 and a deeper look into modules Ranges ● Apply algorithms of STL on containers ○ connect them with pipe operator ● Use infinite data streams auto children_names = all_people | filter([](const auto& person) { return person.age < 14; }) | transform([](const auto& person) { return person.name; }) | to_vector; https://vector-of-bool.github.io/2019/10/21/rngs-static-ovr.html 10
- 11. Overview of C++20 and a deeper look into modules Modules ● Alternative to header and implementation files ○ can halve the number of files in the code base ● No more include guards and/or #pragma once ○ But you can also separate between interface and implementation ● Faster compilation times?! ○ “Reduce build times due to not reparsing large header files” ■ https://gcc.gnu.org/wiki/cxx-modules ○ http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1441r1.pdf ● Isolation of preprocessor macros ● Better way to express which parts of a library are exported https://vector-of-bool.github.io/2019/03/10/modules-1.html 11
- 12. Overview of C++20 and a deeper look into modules Modules > Names module-name: [module-name-qualifier] identifier ; module-name-qualifier: identifier "." | module-name-qualifier identifier "." ; => speech | speech.english 12
- 13. Overview of C++20 and a deeper look into modules Modules > Declaration module-declaration: ["export"] "module" module-name [module-partition] [attribute-specifier-seq] ";" ; module-partition: ":" module-name ; => export module example; 13
- 14. Overview of C++20 and a deeper look into modules Modules > Partitions and “Submodules” Partitions export module speech; export import :english; export import :spanish; “Submodules” → Separate modules export module speech; export import speech.english; export import speech.spanish; 14
- 15. Overview of C++20 and a deeper look into modules Modules > Interfaces hello.cppm export module hello; export const char *greet() { return "Hello, world!"; } 15
- 16. Overview of C++20 and a deeper look into modules Modules > Interfaces and Implementations hello.cppm export module hello; export const char *greet(); hello.cpp module hello; const char *greet() { return "Hello, world!"; } 16
- 17. Overview of C++20 and a deeper look into modules Modules > What can be exported? ● namespace ● class ● struct ● non-static variables/constants ● ... Understanding C++ Modules: Part 2: export, import, visible, and reachable 17
- 18. Overview of C++20 and a deeper look into modules Modules > Interoperability Every compiler uses it’s own binary format. You can not interchange the precompiled modules. https://www.reddit.com/r/cpp/comments/d5dxr3/do_c20_modules_have_a_st andard_binary_format_if/ 18
- 19. Overview of C++20 and a deeper look into modules Compiler support TL;DR: WIP https://en.cppreference.com/w/cpp/compiler_support https://clang.llvm.org/cxx_status.html https://gcc.gnu.org/projects/cxx-status.html https://docs.microsoft.com/en-us/cpp/overview/visual-cpp-language-conform ance?view=vs-2019 19
- 20. Overview of C++20 and a deeper look into modules Resources ● https://isocpp.org/ ● http://www.open-std.org/jtc1/sc22/wg21/docs/papers/ ● https://en.wikipedia.org/wiki/C%2B%2B20 ● https://www.reddit.com/r/cpp/comments/cfk9de/201907_cologne_iso_c_committee_trip_report_the/ ● https://docs.microsoft.com/en-us/cpp/cpp/cpp-language-reference ● https://en.cppreference.com/w/ ● https://vector-of-bool.github.io/ ● https://blog.panicsoftware.com/ ● http://modernescpp.com/ 20