Assume a deleted constructor is added to std::string_view as following:

// Cannot construct a string_view from a temporary string
string_view(string const &&) = delete;

With this change, the following code would fail at compile time:

// You can't do this anymore
std::string_view sv = std::string{"A"} + std::string{"B"};

However this wouldn’t:

// Oops
std::string_view sv = (std::string const &)(std::string{"A"} + std::string{"B"});

What can be done in string to forbid the result of the concatenation to be converted into a string const & (which doesn’t extend the lifetime of the result, and thus the string_view is dangling).