Suppose I have the following type:
struct container {
boost::optional optional() const {
return value_;
}
private:
boost::optional value_;
};
struct value_wrapper {
value_wrapper(const container& c) : c_(c) {}
operator uint16_t () { return 1; }
operator boost::optional() { return c_.optional(); }
private:
const container& c_;
};
And that I have the following function:
value_wrapper value(const container& c) {
return value_wrapper(c);
}
The following used to work in MSVC 2010:
container c;
// leave c.value_ alone.
boost::optional some_value =
value(c);
assert(!some_value);
Now with Boost 1.56, this breaks because the constructor for
some_value from a temporary optional is now marked explicit.
What is the work-around for the previous behavior to be regained? All
the following changes cause the assertion to fail:
boost::optional some_value(value(c));
assert(!some_value); // some_value's constructor will use the
uint16_t conversion operator, therefore some_value == 1
boost::optional some_value =
static_cast >(value(c));
assert(!some_value); // same problem as above, the temporary created
will favor the uint16_t conversion operator
Help?
PS. For better context, see
https://github.com/cpp-netlib/cpp-netlib/blob/0.11-devel/boost/network/proto...
