on Wed Aug 13 2008, "Stjepan Rajko" <stipe-AT-asu.edu> wrote:
On Wed, Aug 13, 2008 at 11:54 AM, David Abrahams <dave@boostpro.com> wrote:
Testing is a good suggestion, but I don't have the time right now to do that :-) I'm not necessarily interested in replicating all Boost.Parameter features. I'm quite happy with the fusion-based solution as a simple one.
Okay, so what are you trying to accomplish?
Being able to have named parameters and not using Boost.Parameter.
Well, then I'm afraid that Boost.Parameter can never help you :-)
Well, at the time we redesigned the library, I encouraged Daniel Wallin to look into whether we could gain anything by using fusion, because the fundamental data structure we use is like a fusion map. He said we couldn't gain anything significant, and at the time I took his word for it. The entire code corresponding to fusion::map is contained in boost/parameter/aux_/arg_list.hpp. The rest of the library consists primarily of functionality you're not providing.
From what you're saying, it could be that our approaches are similar but using a different map type. Using the fusion-based approach, I can do this:
class named_constructable { public: // a macro could extend the number of parameters if desired template<typename FM0, typename FM1> named_constructable(const FM0 &a0, const FM1 &a1) { // this could be done lazily... map<field::label, field::size>::type args = a0 & a1;
label = args.at<field::label>(); size = args.at<field::size>(); } std::string label; int size; };
BOOST_AUTO_TEST_CASE( test_multi_param_construction ) { named_constructable constructed(label_ = "hello", size_ = 1); BOOST_CHECK_EQUAL(constructed.label, "hello"); BOOST_CHECK_EQUAL(constructed.size, 1); }
If our approaches are similar, that would suggest Boost.Parameter could do the same.
With Boost.Parameter it would look like: class named_constructable { public: // a macro could extend the number of parameters if desired template<typename FM0, typename FM1> named_constructable(const FM0 &a0, const FM1 &a1) { label = (a0,a1)[_label]; size = (a0,a1)[_size]; } std::string label; int size; }; But if you use the recommended method of building constructors, Boost.Parameter also supports: named_constructable x0("hello", 1); named_constructable x0("hello", _size=1); named_constructable x0(_label="hello", _size=1); named_constructable x0(_size=1, _label="hello"); and in this case (using deduced parameters), even named_constructable x0(1, "hello");
I'm just saying, if you're going to make comparisons of the two libraries, they should be informed comparisons and not speculation.
Well, I tried to make sure that my speculations were qualified as such (and I consider speculation to be a valid component of discussion). If my speculations came across as assertions, I apologize.
They didn't, but I did find your presumption that we hadn't already gone over this ground in designing the library rather... premature. -- Dave Abrahams BoostPro Computing http://www.boostpro.com