The move `String(Value&&)` constructor tries to partially move `String`
values from a `Value` type. However, since there was no an appropriate
`Value::Get<T>()` implementation that binds to the requested move
operation, the compiler will actually not move the value but copy it
instead as the only available implementation of `Value::Get<T>()`
returns a const reference `const T&`. This commit adds a new overload
that returns a non-const reference and allows to optionally move the string
value of a Value type.
The Icinga DB code performs intensive operations on certain STL containers,
primarily on `std::vector<String>`. Specifically, it inserts 2-3 new elements
at the beginning of a vector containing thousands of elements. Without this commit,
all the existing elements would be unnecessarily copied just to accommodate the new
elements at the front. By making this change, the compiler is able to optimize STL
operations like `push_back`, `emplace_back`, and `insert`, enabling it to prefer the
move constructor over copy operations, provided it is guaranteed that no exceptions
will be thrown.
Boost.Beast changed the signature of
boost::beast::http::basic_fields::set in version 1.74 so that no longer
allows passing an icinga::String instance as value. This adds a
conversion function so that it works again.
