From: "Richard Peters" <r.a.peters@student.tue.nl>
The bigint type proposed for the C++ standard library does not permit
use of expression templates. Using expression templates has a positive and a negative aspect: A significant speedup can be gained using expression templates. The downside is that templates cannot deduce the correct type of expressions, for example: template<class T> void f(T a, T b) will not work when invoked as f(x + y, x - y), because x + y returns an object of type different from x - y. Because the C++ standard library proposal specifies the result type of
operators to be of type const integer, a library implementing that
From: "Rob Stewart" <stewart@sig.com> the the proposal
cannot use expression templates.
PMFJI, but I wonder whether this would work:
PMFJI... I have no clue what it means, sorry.
template <typename T, typename U> void f(T a, U b) { typedef typename <magical_incantation<T, U>::type V; f_impl<V>(a, b); }
a and b can have different types, but then magical_incantation computes a common type to which both can be converted and the implementation function can be invoked with that type.
I may be off base, and you may have already tried this approach, but I just wanted to mention it if it could help.
Oh, there are a few ways in which you can perform computations with the expression templates, but that was not what I meant. My point was: If you specify the result of operators + and - to be big_integer, then expression templates cannot be made to work, because then those operators return types other than big_integer. User code may depend on the specification that those operators do return big_integers. Therefore, any implementation satisfying the requirements of the C++ standard library proposal will miss the possible speedincrease gained by the use of expression templates. best regards, Richard Peters