boost::core::string_view gives ambiguous error

[Spongman]

(1.84 gcc 13.2)

upgrading boost from 1.75 to 1.84 breaks existing code that boils down to:

#include <boost/core/detail/string_view.hpp>

struct Foo
{
    Foo(std::string_view f) {}
    Foo(const std::string& f) {}
};

int main() {
    Foo{std::string_view()};         // works
    Foo{boost::core::string_view()}; // fails

    //Foo{boost::beast::http::fields{}.find("")->value()}; // same failure, works in 1.75
}

https://godbolt.org/z/8TKfP6Pj8

<source>: In function 'int main()':
<source>:11:39: error: call of overloaded 'Foo(<brace-enclosed initializer list>)' is ambiguous
   11 |         Foo{boost::core::string_view()};
      |                                       ^
<source>:6:9: note: candidate: 'Foo::Foo(const std::string&)'
    6 |         Foo(const std::string& f) {}
      |         ^~~
<source>:5:9: note: candidate: 'Foo::Foo(std::string_view)'
    5 |         Foo(std::string_view f) {}
      |         ^~~
Compiler returned: 1

it used to work with BOOST_BEAST_USE_STD_STRING_VIEW. how do I get it to use std::string_view like before?

[pdimov]

Support for BOOST_BEAST_USE_STD_STRING_VIEW was removed 2 years ago and I don't think that the maintainers of Beast will be willing to reinstate it, so I don't think you can get Beast to use std::string_view like before.

core::string_view does convert to both std::string and std::string_view, so the ambiguity is legitimate. It might be possible to fix; I'll have to think about it.

The easiest fix from your side (which may not be applicable) would be to simply remove the constructor taking std::string const& and rely on the std::string_view constructor for std::string arguments. I don't know if that'll work for you, though; maybe you have legitimate reasons for having the std::string const& constructor (e.g. guaranteed null termination).

[Spongman]

no, that doesn't work. Foo is in a 3rd-party library that I can't change, and that overload supports implicit conversion, basically:

    [](const Foo&){}(std::string{});

super confusing to me why std is being deprecated.

[pdimov]

What's the actual Foo?