C++20 introduced the *std::span* which makes it easier to deal
with continuous rage. Especially the subview facilities: *first*, *last*
and *subspan*. I wonder if we can add *first* and *last* function to
*std::string_view*, then we can generate the *substr* more intuitively
and less fallible:

static_assert("hello world"sv.first(5) == "hello");


Thanks for your reply!