id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
9497,mpq_rational asserts when used in variant,András Kucsma <r0maikx02b@…>,John Maddock,"The following code fails with an assertion:
{{{#!C++
#include <boost/variant.hpp>
#include <boost/multiprecision/gmp.hpp>
 
struct Foo {
	Foo() {}
	Foo(const Foo&) {}
};
 
int main() {
	typedef boost::multiprecision::mpq_rational Num;
	typedef boost::variant<Foo, Num> Variant;
 
	Variant x = Num(2);
	Variant y = std::move(x);
 
	x = Foo();
}
}}}
Assert text:
{{{
test: /usr/local/include/boost/multiprecision/gmp.hpp:1947: __mpq_struct (& boost::multiprecision::backends::gmp_rational::data())[1]: Assertion `m_data[0]._mp_num._mp_d' failed.
Aborted
}}}

Some notes on the code:
* The explicit copy constructor for Foo is necessary
* Replacing mpq_rational with mpz_int or cpp_rational doesn't cause assertion
* Using boost::move without the -std=c++11 flag doesn't assert. (but it does assert with -std=c++11)

Tested on Linux with: 
* g++-4.8.1, g++-4.8.2, clang 3.5 (trunk 197340)
* boost-1.55.0 and trunk revision: 86799
* libgmp 5.1.0

Compiled with the command:
(clan)g++ -std=c++11 main.cpp /usr/local/lib/libgmp.a -O0 -g

The source of the problem could very well be in how variant handles move semantics in C++11 mode.

Note: you can also find this file here:
https://gist.github.com/r0mai/7978397",Bugs,closed,To Be Determined,multiprecision,Boost 1.55.0,Problem,fixed,,antoshkka@…