The previous code works in _some_ STL implementations, namely if
_either_ of the following is true:
1. At least one of the other four STL headers included by json.h
transitively includes <string>, as opposed to just <stringfwd.h>; or
2. The way std::variant is implemented does not require knowing the
inner types' type traits when just naming the std::variant
without yet instantiating any of its member function templates.
On other STL implementations in which neither of the above is true, this
example failed to build with an error such as:
In file included from target/debug/build/example-d2d484e0c793273c/out/cxxbridge/sources/example/src/main.rs.cc:1:
In file included from target/debug/build/example-d2d484e0c793273c/out/cxxbridge/crate/example/include/json.h:2:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/map:60:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_tree.h:63:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_algobase.h:64:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stl_pair.h:59:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/move.h:57:
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/type_traits:1339:23: error: implicit instantiation of undefined template 'std::basic_string<char>'
__bool_constant<__has_trivial_destructor(_Tp)>>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/type_traits:3214:5: note: in instantiation of template class 'std::is_trivially_destructible<std::basic_string<char>>' requested here
is_trivially_destructible<_Tp>::value;
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/variant:299:5: note: in instantiation of variable template specialization 'std::is_trivially_destructible_v<std::basic_string<char>>' requested here
(is_trivially_destructible_v<_Types> && ...);
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/variant:308:4: note: in instantiation of static data member 'std::__detail::__variant::_Traits<std::monostate, double, std::basic_string<char>, std::vector<json>, std::map<std::basic_string<char>, json>>::_S_trivial_dtor' requested here
_S_trivial_dtor && _S_trivial_move_ctor
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/variant:689:45: note: in instantiation of static data member 'std::__detail::__variant::_Traits<std::monostate, double, std::basic_string<char>, std::vector<json>, std::map<std::basic_string<char>, json>>::_S_trivial_move_assign' requested here
_Move_assign_base<_Traits<_Types...>::_S_trivial_move_assign, _Types...>;
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/variant:692:28: note: in instantiation of template type alias '_Move_assign_alias' requested here
struct _Variant_base : _Move_assign_alias<_Types...>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/variant:1318:15: note: in instantiation of template class 'std::__detail::__variant::_Variant_base<std::monostate, double, std::basic_string<char>, std::vector<json>, std::map<std::basic_string<char>, json>>' requested here
: private __detail::__variant::_Variant_base<_Types...>,
^
target/debug/build/example-d2d484e0c793273c/out/cxxbridge/crate/example/include/json.h:33:63: note: in instantiation of template class 'std::variant<std::monostate, double, std::basic_string<char>, std::vector<json>, std::map<std::basic_string<char>, json>>' requested here
std::variant<std::monostate, number, string, array, object> value;
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/stringfwd.h:74:11: note: template is declared here
class basic_string;
^
This constructor maps to `String::from_utf8_lossy` or
`String::from_utf16_lossy`. It's useful in situations where producing a
slightly garbled string on invalid Unicode data is preferable to
crashing the process, e.g. when passing error messages from C++ to Rust.
Based on the model of #951, which added `Vec<T>::clear`. The `truncate`
method is the more general form of clear.
(If we wanted to, we could delete the binding for `clear` and implement
`clear` as a call to `truncate(0)` on the C++ side, but seemed worth
leaving in in case the Rust `clear` implementation one day gets
smarter.)
The first argument of the closure is actually the context, not the
sender. Rename it to `context` to make it clearer. Was slightly confused
the first time I read it.
