"Ovanes Markarian" writes:

Hello,

can someone tell me what exactly a parameter State in the mpl::accumulate means.

It's exactly like the second form of std::accumulate http://www.sgi.com/tech/stl/accumulate.html

After the evaluation is finished, which type is returned by accumulate? State?

No. For example, if the elements are (e1, e2, e3), the type returned is mpl::apply< binary_op , mpl::apply< binary_op , mpl::apply::type , e2 >::type , e3 >::type or, in pseudocode, binary_op( binary_op( binary_op(State,e1), e2), e3)

Which types are passed to the binary ForwardOp?

See above.

I do not exactly understand this example:

typedef vector types;

typedef accumulate< types , int_<0> , if_< is_float<_2>,next<_1>,_1 > >::type number_of_floats;

The whole expression returns a type-representation of the number of instances of "float" in the sequence "types." State is int_<0>, a type-representation of the number zero. binary_op is lambda expression that returns either its first argument or a type-representation of its first argument plus one. <plug> BTW, http://www.boost-consulting.com/mplbook has a pretty good explanation of this material. </plug> HTH, -- Dave Abrahams Boost Consulting www.boost-consulting.com