Peter Dimov wrote:
Eric Niebler wrote:
Although I don't know all the details of bind and lambda, I had hoped that _1 and _2 would be abstract proto entities, such that
_1 == _2
creates an expression template like:
equal< terminal< arg<1> >, terminal< arg<2> > >
which is a generic, abstract representation of an equals expression with two placeholders. Can't bind and lambda both be implemented to recognize such a type and do the appropriate thing with it?
Possibly, if they are made to honor is_bind_expression specializations and result_of, if is_bind_expression reports true for the above type, if the above is a function object that actually returns x == y, and if result_of works for it.
Yes, that can all be made to work without much difficulty.
The only minor complication is that for the placeholders and expressions containing them, operator() must evaluate the expression rather than create a larger expression template. But that's trivial to do with proto.
Trivial? :-) Are you assuming variadic templates
No. and decltype? No, but I *am* assuming Boost.Typeof. Consider _9 -
_4 as one simple example.
Either way, if proto does evaluate, there would be no need for most of Lambda.
Precisely. :-) -- Eric Niebler Boost Consulting www.boost-consulting.com