Reading a line or word at a time

Reading from standard input one line at a time is a very common task in simple scripts, and most scripting languages make it a one-liner. For example, in Python:

    for line in sys.stdin:
    # preserves trailing newlines
    process(line)

And in Perl:

    while (<>) {
      # preserves trailing newlines
      process($_);
    }

In C++, the task is almost as easy. Notice that C++'s std::getline function, unlike the other languages' idioms, removes the trailing newline (if any) from each line it reads:

    std::string line;  
    while (std::getline(std::cin, line)) {
      // automatically chomps trailing newlines
      process(line);
    }

In each of these cases, the entire input never lives in memory at once; we are indeed "streaming" the lines through our program in an efficient manner. (And the std::getline function is allocator-aware; if we absolutely need to avoid heap allocation, we can exchange std::string line for std::pmr::string.) The process...