I realize that this message may have not passed the spam filters. Can someone comment on the changes in Boost.Optional in 1.56.0 breaking existing code? On Mon Aug 18 2014 at 8:10:52 PM Dean Michael Berris <dberris@google.com> wrote:
Suppose I have the following type:
struct container { boost::optional<uint16_t> optional() const { return value_; } private: boost::optional<uint16_t> value_; };
struct value_wrapper { value_wrapper(const container& c) : c_(c) {} operator uint16_t () { return 1; } operator boost::optional<uint16_t>() { 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<uint16_t> 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<uint16_t> some_value(value(c)); assert(!some_value); // some_value's constructor will use the uint16_t conversion operator, therefore some_value == 1
boost::optional<uint16_t> some_value = static_cast<boost::optional<uint16_t> >(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/protocol/http/algorithms/linearize.hpp#L145
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