Re: [Boost-users] boost::variant & c++11

Thanks for taking a look. I checked, and on my system, you're right: adding a non-const conversion operator allows the code to compile with c++11 and boost 1.53.0. Although I'm not sure why adding a non-const conversion operator would be expected to ensure the implicit conversion happens. I would expect the non-const conversion operator couldn't be called on a temporary object (maybe things are different when we have rvalue references?) In any case, the "convertible" in this reproducer is standing in for a class from Boost.Python, so I can't just add the extra non-const conversion operator to work around the problem. - bryan On Wed, May 15, 2013 at 1:54 PM, Antony Polukhin wrote:

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Hi Antony - Perhaps it is compiler dependent. Which version of MSVC did you reproduce the error with? Does that version have c++11 support enabled (in

2013/5/15 Bryan Catanzaro : particular,

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rvalue references) As I said, with Boost 1.48.0, this code works with g++ 4.6 and 4.7. With 1.53.0, it works with g++ 4.6 and 4.7 only if c++11 support is turned off. If c++11 support is turned on, the code does not work. I've attached a shell script that compiles the attached code with the cross product of {(g++4.6, g++4.7), (boost1.48, boost1.53), (noc++11, yesc++11)}. As you can see from test.txt, the error happens only with boost 1.53 and c++11 support.

- bryan

Exactly the same things happen on GCC-4.5 and Clang-3.0.

But what is more interesting here: convertible c; const convertible& cc = c;

// Always compiles, using any flags, compiler and Boost version my_variant y = cc; my_variant y1 = static_cast(c); my_variant y2 = static_cast<const convertible>(c);

// Always fail to compile, using any flags and Boost version // my_variant z = c; // my_variant y3 = static_cast(c);

Tested on clang, gcc4.5, gcc 4.6, gcc4.7 on Boost 1.48 and Boost 1.53 with and without C++11 flags.

If we modify `convertible`:

struct convertible { operator my_variant() { return my_variant(); }

operator my_variant() const { return my_variant(); } };

Then ALL the tests pass well, even the commented out ones. Even `my_variant y4 = static_cast(c);` works well.

I'll test it tomorrow on Visual Studio 11 once more and investigate issue futher.

-- Best regards, Antony Polukhin