23 Ranges library [ranges]

23.8 Range adaptors [range.adaptors]

23.8.7 Join view [range.join]

23.8.7.1 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
]