24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.10 Join view [range.join]

24.7.10.1 Overview [range.join.overview]

join_­view flattens a view of ranges into a view.
Example
:
vector<string> ss{"hello", " ", "world", "!"};
join_view greeting{ss};
for (char ch : greeting)
  cout << ch;                                   // prints: hello world!
— end example
 ]