Returns the number of elements.

Equivalent toreturnstd::apply
       (
           [](auto...sizes)
           {
               using CT=ranges::common_type_t<decltype(sizes)...>;
               return(make-unsigned-like-t <CT>(sizes)+ ...);
           },
           tuple-transform (ranges::size, views_ )
       );.

[edit]Return value

As described above.

[edit]Complexity

Constant.

[edit]Notes

The complexity ofconcat_view is constant time (even though in some cases it is a linear function of the number of ranges it concatenates which is a statically known parameter of this view) because time complexity as required by the ranges concepts are formally expressed with respect to the total number of elements (the size) of a given range, and not to the statically known parameters of that range.

[edit]Example

#include <cassert>#include <forward_list>#include <list>#include <ranges> int main(){constexprstaticauto a={1,2};constexprstaticauto b={1,2,3};constexprstaticauto c={1,2,3,4}; constexprauto con{std::views::concat(a, b, c)};    static_assert(std::ranges::sized_range<decltype(con)>);    static_assert(con.size()==2+3+4); std::forward_list d= b;    static_assert(not std::ranges::sized_range<std::forward_list<int>>);constauto cat{std::views::concat(b, c, d)};    static_assert(not std::ranges::sized_range<decltype(cat)>);//  auto x = cat.size(); // error: cat is not sized_range because of d std::list e= c;constauto dog{std::views::concat(a, b, e)};    static_assert(std::ranges::sized_range<decltype(dog)>);assert(dog.size()==2+3+4);}

[edit]See also

• In other languages

• Deutsch
• Español
• 日本語
• Русский
• 中文