At Sun, 26 Sep 2010 22:31:54 -0400, Eric Niebler wrote:
On 9/26/2010 9:44 PM, David Abrahams wrote:
On Sep 26, 2010, at 8:55 AM, Eric Niebler wrote:
On 9/25/2010 1:24 PM, David Abrahams wrote:
On Sep 24, 2010, at 11:51 PM, Eric Niebler wrote:
On 9/24/2010 9:37 PM, David Abrahams wrote:
Haha! No, not at all. Let's rephrase the problem a bit. If we still had C++0x concepts, what would the concept SpiritParser look like, such that we could define spirit::qi::rule::operator= such that it required its RHS to satisfy the SpiritParser concept?
That's easy to answer; just look at the operations that operator= et. al expect of such a type. Wouldn't SpiritParser just be some simple refinement of Callable?
No. rule::operator= expects SpiritParser to be a strongly-typed tree.
Meaning? Spell it out and you have your requirements.
Meaning:
+ If the topmost node has tag-type "plus", there must be exactly one child node that models SpiritParser + If the topmost node has tag-type "shift_right", there must be exactly two child nodes that model SpiritParser, + If the topmost node has tag-type "subscript", there must be a left node that models SpiritParser and a right node that models PhoenixLambda, ... etc, etc, etc, ad nauseum
No offense, but did you really answer the question I asked? Does operator= actually use those requirements? On the face of it, it just seems a lot more likely that it simply requires its RHS to also be a SpiritParser.
How do I express that as a concept?
Summoning up my dim memory of proposed concept notation (so there are guaranteed nits to pick), that might translate into something like: concept SpiritNode<typename Node, typename Tag> { } template <class Node> concept_map SpiritNode<typename Node, plus> { requires SameType<Node::children,int_<1> >; typename child_t; requires SpiritParser<child_t>; child_t child; } template <class Node> concept_map SpiritNode<typename Node, shift_right> { requires SameType<Node::children,int_<2> >; typename child1_t; requires SpiritParser<child1_t>; typename child2_t; requires SpiritParser<child2_t>; child1_t child1; child2_t child2; } template <class Node> concept_map SpiritNode<typename Node, subscript> { requires SameType<Node::children,int_<2> >; typename child1_t; requires SpiritParser<child1_t>; typename child2_t; requires PhoenixLambda<child2_t>; child1_t child1; child2_t child2; } concept RHSOfAssign<typename X> { typename tag_type; // Every RHSOfAssign has an associated tag_type requires SpiritNode<X, tag_type>; } This isn't really how concepts were "meant to be used," though. -- Dave Abrahams BoostPro Computing http://www.boostpro.com