On 10/05/2010 02:42 PM, Christophe Henry wrote:

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I have 2 fusion containers: a small vector (my_vec) and a bigger set (my_set). I want to overwrite the elements of the set with elements from the vector whenever they have the same type. Sounds simple:

struct update { update(my_set_type& to_overwrite_):to_overwrite(to_overwrite_){} template<typename T> void operator()(T& elt) /*const?*/ { boost::fusion::at_key<T>(to_overwrite)=elt; } my_set_type& to_overwrite; };

boost::fusion::for_each(my_vec,update(my_set));

Except that this won't compile because the operator() is required to be const, which is sad, because it was very simple.

And it won't compile *with* the const? I don't think the const'ness of the member function affects the const'ness of the referent of to_overwrite.

No, it won't compile ;-)

Hmmm...this simple program compiles for me, as I would expect (g++ 4.4.3): struct X { int& operator()() const { return y; } int& y; }; int main() { int y = 42; const X x = { y }; int& z = x(); return 0; } which suggests to me that the addition of the const qualifier on operator() should be okay... - Jeff