Example of the perils of binding rvalues to const ref

[Szymon Gatner via Digitalmars-d]

On Wednesday, 17 September 2014 at 08:52:58 UTC, Arjan wrote:
> On Tuesday, 16 September 2014 at 15:30:49 UTC, Andrei 
> Alexandrescu wrote:
>> http://www.slideshare.net/yandex/rust-c
>>
>> C++ code:
>>
>> std::string get_url() {
>>    return "http://yandex.ru";
>> }
>>
>> string_view get_scheme_from_url(string_view url) {
>>    unsigned colon = url.find(':');
>>    return url.substr(0, colon);
>> }
>>
>> int main() {
>>    auto scheme = get_scheme_from_url(get_url());
>>    std::cout << scheme << "\n";
>>    return 0;
>> }
>>
>> string_view has an implicit constructor from const string& 
>> (see "basic_string_view(const basic_string<charT, traits, 
>> Allocator>& str) noexcept;" in 
>> https://isocpp.org/files/papers/N3762.html). The function 
>> get_url() returns an rvalue, which in turn gets bound to a
>
> Forgive me my ignorance but  get_url() returns a std::string 
> (on the stack), so its address can be token.
> And iirc the explainer Scott Meyers explained once "iff you can 
> take its address its not a rvalue its a lvalue". So isn't the 
> get_scheme_from_url() not simply holding a const ref to 
> temporary? (which most compiler warn about)
>
> ...Or am I missing the point?
>
>> reference to const and implicitly passed to string_view's 
>> constructor. The obtained view refers to a dead string.
>>
>>
>> Andrei