#include 
#include 
#include 
#include 
int main()
{
    std::vector v = { 1, 2, 3, 4, 5 };
    auto oddnumbersview = v | std::views::filter([](int x) { return x % 2 == 1; });
    for (auto el : oddnumbersview)
    {
        std::cout << el << '
';
    }
}

Explanation: we have a simple vector with some elements. Then we create a view range adaptor on that vector, which filters the numbers in the range. For this, we use the pipe operator |. Only the numbers for which the predicate is true are included. In our case, this means the even numbers are excluded. Then we iterate over the filtered view and print out the elements.gV0拜客生活常识网

Important to note, the underlying vector’s elements are unaffected as we are operating on a view, not on a vector.gV0拜客生活常识网

Let us create an example which creates a view that returns only numbers greater than 2:gV0拜客生活常识网

#include 
#include 
#include 
#include 
int main()
{
    std::vector v = { 1, 2, 3, 4, 5 };
    auto greaterthan2view = v | std::views::filter([](int x) { return x > 2; });
    for (auto el : greaterthan2view)
    {
        std::cout << el << '
';
    }
}

Now, let us combine the two views into one big view by separating them with multiple pipe | operators:gV0拜客生活常识网

#include 
#include 
#include 
#include 
int main()
{
    std::vector v = { 1, 2, 3, 4, 5 };
    auto oddandgreaterthan2 = v | std::views::filter([](int x) { return x % 2 == 1; })
                                | std::views::filter([](int x) { return x > 2; });
    for (auto el : oddandgreaterthan2)
    {
        std::cout << el << '
';
    }
}

This example creates a view range adaptor containing odd numbers greater than two. We create this view by combining two different range views into one.gV0拜客生活常识网

Another ranges adaptors are algorithms. The idea is to have the algorithms overload for ranges. To call an algorithm adaptor we use: std::ranges::algorithm_name(parameters). Example using the std::ranges::reverse() algorithm:gV0拜客生活常识网

#include 
#include 
#include 
#include 
int main()
{
    std::vector v = { 1, 2, 3, 4, 5 };
    std::ranges::reverse(v);
    for (auto el : v)
    {
        std::cout << el << '
';
    }
}

Unlike views, the ranges algorithms modify the actual vector content.gV0拜客生活常识网

40.4.6 Coroutines

A coroutine is a function that can be suspended and be resumed. The ordinary function is a coroutine if it uses any of the following operators in its function body:gV0拜客生活常识网

a. co_await – suspends the execution of the coroutine until some other computation is performed, that is until the coroutine itself resumesgV0拜客生活常识网

b. co_yield – suspends a coroutine and return a value to the callergV0拜客生活常识网

c. co_return – returns from a coroutine and stops its executiongV0拜客生活常识网

20.7 std::span

std::string_view定义的是特定的类型(string)，std::span是与std:string_view相同概念的全部类型的应用。gV0拜客生活常识网

Some containers and types store their elements in a sequence, one next to the other. This is the case for arrays and vectors. We can represent such containers

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