slides chiphogg/cppcon-2023-au-units 12Units library: basic concept // No units library: double distance_m; 1 2 3 4 5 3Units library: basic concept // With units library: Quantity double> distance; // No units library: 1 double distance_m; 2 3 4 5 3.1Units library: basic concept // With units library: Quantity distance; // No units library: 1 double distance_m; distance_m; 2 3 4 5 3.2Units library: basic concept // With units library: Quantity distance; // No units library: 1 double distance_m; 2 3 4 5 3.3Aurora InnovationAurora InnovationFlashback:

quantities and units library The future is here 2CppCon 2024: Improving our safety with a quantities and units library The future is here 3CppCon 2024: Improving our safety with a quantities and units library 2024: Improving our safety with a quantities and units library Tactical Flight Computer 5CppCon 2024: Improving our safety with a quantities and units library Tactical Flight Computer 6• A major concern safer high-level abstractions in the library CppCon 2024: Improving our safety with a quantities and units library C++ safety 7• Many C++ engineers are expected to write life-critical so�ware today • Experience

Mateusz Pusz September 15, 2020 A Physical Units Library For the Next C++CppCon 2020 | A Physical Units Library For the Next C++ Motivation, Existing Practice, Challenges... 21 Quick Start 2 Strong Experience 5 Framework Basics 6 Environment, compatibility, next steps CppCon 2020 | A Physical Units Library For the Next C++ Agenda 31 Quick Start 2 Strong Interfaces 3 As fast as (or even faster) compatibility, next steps CppCon 2020 | A Physical Units Library For the Next C++ Agenda In Q&A please refer to the slide number. 3CppCon 2020 | A Physical Units Library For the Next C++ QUICK START 4// simple

wikimedia.org/w/index.php?curid=49765027 https://www.vintagesynth.com/misc/tassman4.phpWhat do units matter?What do units matter? ...making it to Mars.Mars climat orbiter Launch December 11, 1998 Cost $327 newton-secondsWhat do units matter? … “is it supposed to make sound?”Not life and death, but audio bugs can be dangerous ● Hearing loss ● Damaged speakers ● Crashes during live performanceI tried boost::units… …and …and gave up.My journey to mp-units… https://github.com/mpusz/mp-unitsMy journey to to mp-units… ● P1386 A Standard Audio API for C++: Motivation, Scope, and Basic Design ○ Wanted standard vocabulary

Advance to the next state while (curr > ERR) //- Loop over subsequent units { if (pSrc < pSrcEnd) { unit = *pSrc++; //- Cache the current code unit to the next state while (curr > ERR) //- Loop over subsequent code units { ... } return curr; }Copyright © 2020 Bob Steagall K E W B C O M P U T I N G 39 CppCon 2020 - Adventures to the next state while (curr > ERR) //- Loop over subsequent code units { ... } return curr; }Copyright © 2020 Bob Steagall K E W B C O M P U T I N G 40 CppCon 2020 - Adventures

foxtrot.cxx golf.cxx alpha.o bravo.o charlie.o delta.o foxtrot.o golf.o Module interface units need to be compiled before any of the importers import fmt; fmt.cxx fmt.pcm fmt.oCompilation time included in many translation units, the compiler does the same job repeatedly ○ Downsides w.r.t. the preprocessor ● Using import introduces a dependency order between translation units ○ The BMI for module module interface units must be generated before any importer is translated - have to work out build order ○ But better isolation between modules and importers ○ Potential for improved compilation times●

Rule is your friend – Named modules provide ODR guarantees, by design – Header files and header units require (expensive) incomplete ODR checks, and demand complete trust 4 (C) Dos Reis & DaCamara; principle ▪ Headers vs header units vs named modules ▪ Spectacular improvement in compile-time performance 23 (C) Dos Reis & DaCamara; CppCon 2021Headers vs header units vs named modules #include needed main() { std::cout << "Hello, World!\n"; } (C) Dos Reis & DaCamara; CppCon 2021Headers vs header units vs named modules #include needed headers import needed headers import std #include “all_std

Look at the event service ! ComplaintsMONITORING 142 ⊡ Started reading events for specific units, but it was uncomfortable. ⊡ Two students proposed writing a script to retrieve the events and file (sort, filter, plot). How I started:MONITORING 143 ⊡ Started reading events for specific units, but it was uncomfortable. ⊡ Two students proposed writing a script to retrieve the events and file (sort, filter, plot). How I started:MONITORING 144 ⊡ Started reading events for specific units, but it was uncomfortable. ⊡ Two students proposed writing a script to retrieve the events and

○ version, revision ○ sets ● Sets ○ family-name, name ○ visible-sets, translation-units ● Translation units ○ object, source, work-directory ○ arguments, baseline-arguments, local-arguments ○ performance metrics 21Build Databases: Sets ● Each set has: ○ Name ○ Family name ○ Translation units ○ Visible sets (names of sets that provide modules that may be imported in this set) ● In CMake ● Using “visible sets”, the target graph can be known by tooling 22Build Databases: Translation Units ● This is where existing compile database entries start showing up ○ Object (uniqueness constraint)

pn, int quantity); add_to_inventory(90042, 2); // OK. Add 2 units of part 90042 add_to_inventory(2, 90042); // Oops! Add 90042 units of part add_to_inventory(01773, 1); // Oops! Add 1 unit of part pn, int quantity); using namespace part_literals; add_to_inventory(90042_part, 2); // OK. Add 2 units of part 90042 add_to_inventory(2, 90042_part); // Argument mismatch error! Won't compile. add_to "eeec1114-8078-49c5-93ca-fea6fbd6a280"_UUID; // OK UUIDv4 Bad = "123x"_UUID; // Error: bad UUID formatPhysical units 10/26/21 Pablo Halpern, 2021 (CC BY 4.0) 55 namespace si_literals { constexpr Distance operator""_m