Markus Werle wrote:
Eric Niebler <eric <at> boost-consulting.com> writes:
The reason I ask is because if you use expr<>, you are limited to BOOST_PROTO_MAX_ARITY elements, which is probably too low. And bumping BOOST_PROTO_MAX_ARITY gets expensive.
Alarm level red: You have measurements: what is the implication of setting BOOST_PROTO_MAX_ARITY to values greater than 10 considering compile time?
Here are the compile times for libs/xpressive/test/test2.cpp, a fairly rigorous workout for Proto, for different max arities. Arity Compile time (sec) ------------------------- 5 5.132 10 5.725 15 6.895 20 8.517 25 11.091 30 14.492 35 18.922 40 25.100 As you can see, beyond 20 things begin to get bad, but not dramatically so. One of the big sources of slow-down is the operator() overloads on expr<> ... there are N specializations of expr<>, and each one has N overloads of operator(). That's O(N^2) growth. With a variadic operator(), I should be able to knock that down to O(N). In picking a max arity for a DSEL, I think we reach the limits of human readability (a function that takes 20 arguments?! Really?) before we reach Proto's breaking point. -- Eric Niebler Boost Consulting www.boost-consulting.com