Chocolate lover, Committee member, Comma supervisor, C++ nerd here to talk about CTAD• John Lakos • Vittorio Romeo • Rostislav Khlebnikov • Alisdair Meredith • An extended team Deduction (CTAD) and how it makes our life easierWhat is in this talk • What is Class Template Argument Deduction (CTAD) and how it makes our life easier • The principles of how CTAD worksWhat is is in this talk • What is Class Template Argument Deduction (CTAD) and how it makes our life easier • The principles of how CTAD works • Things to be aware of when it comes to CTADWhat isn’t in

algorithms • Efficient parallel operations between work items • Class template argument deduction (CTAD) and template deduction guides • Simplified class template instantiation • Simplified use of Accessors object describing the number of elements in a multi- dimensional space SYCL 2020: Buffers have CTAD so no longer require explicit template parameters #include int main(int argc, char access mode is used by the SYCL runtime to manage data dependencies SYCL 2020: Accessors have CTAD and tags so no longer require explicit template parameters #include int main(int

reference to it. Its destructor unlocks the mutex. In C++17 and later, lock_guard can be used with CTAD, as shown in numTokensAvailable().A “mutex lock” is a resource ● A new’ed T* is a resource, in the It can take multiple mutexes “at once,” although naming the resulting type is quite ugly without CTAD. size_t numTokensAvailable() const { std::scoped_lock lk(mtx_); return tokens_ std::barrier, unlike std::latch, is a class template! ○ The template parameter has a default, so CTAD permits you to say barrier b; in most places. But I recommend barrier<>, just like less<>. ○ It

{ using std::swap; while(b != e) { --e; if(b == e) return; swap(*b, *e); ++b; } } 181 // CTAD! vector v{ 2,3,5,7,11 }; rev(begin(v), end(v));Sometimes unnoticed upsides of iterators template { using std::swap; while(b != e) { --e; if(b == e) return; swap(*b, *e); ++b; } } 182 // CTAD! list v{ 2,3,5,7,11 }; rev(begin(v), end(v));Sometimes unnoticed upsides of iterators template CTAD! deque v{ 2,3,5,7,11 }; rev(begin(v), end(v));Sometimes unnoticed upsides of iterators template

somewhere in contiguous storage (ex: std::vector) vector cov_mtx_data // Cov Matrix (Sigma) – Use CTAD { 0.01263, 0.00025, -0.00017, 0.00503, 0.00025, 0.00138, 0.00280, 0.00027, -0.00017, 0 Daniel Hanson CppCon 2024 28• Recall: calculate as 𝝎𝑻(𝚺𝝎): // mdspan views of data (can use CTAD): stdex::mdspan md_cov_mtx{cov_mtx_data.data(), stdex::extents{n, n}}; stdex::mdspan md_wgts{omega

#include std::variant v = 'W'; variant v{'W'}; 37 Or, using CTAD and/or direct-initialization, but personally I don’t recommend either...Recursive default-construction std::tuple t = std::make_tuple(1, 2, 3); return std::make_pair(42, false); } 58 C++17 CTAD alert! Function templates make_pair and make_tuple will deduce their argument types. Distinguish

each of the mutexes Not copyable or movable No member functions or other operations C++17 Uses CTAD to deduce class template arguments std::scoped_lock lock(mutex_a, mutex_b); https://en.cppreference unlock() on the mutex Not copyable or movable No member functions or other operations Can’t assume CTAD is available std::lock_guard lock(mutex_a); https://en.cppreference.com/w/cpp/thread/lock_guardCppCon

preview::ranges; views::iota('A', 'E') | views::enumerate | ranges::to(); // While evaluating CTAD, std::tuple to std::pair is found to be valid thus // deduced to std::map with additional

7879Runtime initialization 808182Compile Time Analysis to a array 83Execution is simple 84Aside: CTAD for std::array size (since C++20) 85Performance Measurement The experiment was a failure  Or wasn’t

Polymorphism 21 template struct Overload : Ls ... { using Ls::operator( )...; }; // CTAD (Class Template Argument Deduction) // needed prior to C++ 20 template Overload(Ls