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Latest C ++ Development News

Recently, in the Finnish city of Oulu, the meeting of the WG21 international working group on C ++ standardization ended, in which Yandex employees officially participated for the first time. It approved a draft version of C ++ 17 with a variety of new classes, methods and useful innovations of the language.



During the trip, we dined with Bjarne Stroustrup , rode in the elevator with the Coat of Arms Sutter , shook hands with Behman Daves , went out for air and breathed with Vincent Bothe , discussed online games with Gor Nishanov , were at the reception at the Oulu city hall and talked to the mayor. We also, together with everyone from 8:30 to 17:30, worked on the new C ++ standard, often gathering at 20:00 to work four more hours and have time to add a couple of good things.
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Now we are ready to share with you the "goodies" of the new standard. Anyone wishing to have a look at the multi-threaded algorithms, new containers, unusual capabilities of old containers, “syntactic sugar” of the new wonderful C ++, please under the cat.

if constexpr ( condition )


In C ++ 17, it was possible to perform if at the compilation stage:

template <std::size_t I, class F, class S>
auto rget(const std::pair<F, S>& p) {
    if constexpr (I == 0) {
        return p.second;
    } else {
        return p.first;
    }
}

. , :

T& container::emplace_back(Args&&...)


emplace_back(Args&&...) sequence :
// C++11
some_vector.emplace_back();
some_vector.back().do_something();

// C++17
some_vector.emplace_back().do_something();

std::variant<T...>


: std::variant<T...> — union, .
std::variant<int, std::string> v;
v = "Hello word";
assert(std::get<std::string>(v) == "Hello word");
v = 17 * 42;
assert(std::get<0>(v) == 17 * 42);

boost::variant, :



, ExecutionPolicy. , , :
std::vector<int> v;
v.reserve(100500 * 1024);
some_function_that_fills_vector(v);

//   
std::sort(std::execution::par, v.begin(), v.end());

: , ExecutionPolicy, , std::terminate():
std::sort(std::execution::par, v.begin(), v.end(), [](auto left, auto right) {
    if (left==right)
        throw std::logic_error("Equal values are not expected"); //  std::terminate()

    return left < right;
});



. push pop():
// C++11
void push(std::multiset<value_type>&& items) {
    std::unique_lock<std::mutex> lock(values_mutex_);
    for (auto&& val : items) {
        //  ,   
        values_.insert(val);
    }

    cond_.notify_one();
}

value_type pop() {
    std::unique_lock<std::mutex> lock(values_mutex_);
    while (values_.empty()) {
        cond_.wait(lock);
    }

    //  ,   
    value_type ret = *values_.begin();
    //  
    values_.erase(values_.begin());

    return ret;
}

// C++17
void push(std::multiset<value_type>&& items) {
    std::unique_lock<std::mutex> lock(values_mutex_);

    //   ,   .
    //    (. #2)
    values_.merge(std::move(items));

    cond_.notify_one();
}

value_type pop() {
    std::unique_lock<std::mutex> lock(values_mutex_);
    while (values_.empty()) {
        cond_.wait(lock);
    }

    //        (. #2)
    auto node = values_.extract(values_.begin());
    lock.unlock();

    //     multiset'
    return std::move(node.value());
}

C++17 , . pop() :
//   rbtree   '' (tree-node)
auto node = values_.extract(values_.begin());

//  values_      ,      node
// values_mutex_    values_.      
//   ,         .
lock.unlock();

//      ,    .  std::move   .
return std::move(node.value());

//

C++17 :


C++17 . , , , :
std::pair<int, double> p(17, 42.0);
std::pair p(17, 42.0);
std::lock_guard<std::shared_timed_mutex> lck(mut_);
std::lock_guard lck(mut_);
std::lock_guard<std::shared_timed_mutex> lck(mut_);
auto lck = std::lock_guard(mut_);

std::string_view


C++17. C++11 , :
// C++11
#include <string>
void get_vendor_from_id(const std::string& id) { //  ,         std::string
    std::cout <<
        id.substr(0, id.find_last_of(':')); //      
}

// TODO:  get_vendor_from_id(const char* id)

C++17 :
// C++17
#include <string_view>
void get_vendor_from_id(std::string_view id) { //   ,   `const char*`, `char*`, `const std::string&`  ..
    std::cout <<
        id.substr(0, id.find_last_of(':')); //     
}

std::basic_string_view std::string_view — , , . Boost, boost::basic_string_ref boost::string_ref.

std::string_view C++17, std::string. <string_view> <string>, std::string_view .

:

: string_view , , , '\0', string_view::data() , - .

if (init; condition)


:
// C++11
void foo() {
    // ...
    {
        std::lock_guard<std::mutex> lock(m);
        if (!container.empty()) {
            // do something
        }
    }
    // ...
}

, . C++17 :
// C++17
void foo() {
    // ...
    if (std::lock_guard lock(m); !container.empty()) {
        // do something
    }
    // ...
}

lock if.

Structured bindings


std::set<int> s;
// ...

auto [it, ok] = s.insert(42); 
//  it —    ; ok - bool   .
if (!ok) {
    throw std::logic_error("42 is already in set");
}
s.insert(it, 43);
// ...

Structured bindings std::pair std::tuple, :
struct my_struct { std::string s; int i; };
my_struct my_function();
// ...

auto [str, integer] = my_function();

...


C++17 :



C++Siberia ++ , , , , .

Source: https://habr.com/ru/post/304510/

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