Re: [Boost-users] [fusion] more trouble with transform

Gennadiy Rozental writes:

Hi,

Now I am trying to perform transform which mutates:

------ #include #include #include #include namespace fusion=boost::fusion;

struct C {};

struct B { C make_c() { return C(); } };

struct make_c { template<typename Sig> struct result;

template <typename T> struct result { typedef C type; }; template <typename T> struct result { typedef C type; };

template <typename T> C operator()(T& t) const { return t.make_c(); } };

int main() { B b1, b2; auto z1 = fusion::make_list( b1, b2 );

auto z2 = fusion::as_list( fusion::transform( z1, make_c() ) );

return 0; } ----

Both gcc and msvc complain like this:

test.cpp:29:46: error: passing ‘const B’ as ‘this’ argument of ‘C B::make_c()’ discards qualifiers.

What am I missing now?

Gennadiy

fusion::transform only accepts cref-qualified sequences. That is why the resulting transform view will be store a reference to z1 const and thus the arguments passed to make_c are const-qualified. https://svn.boost.org/trac/boost/ticket/3446 Construct the transform view by hand and your example should work fine. Christopher