Spirit Rule<>s

From: joel de guzman (isis-tech_at_[hidden])
Date: 2001-05-28 03:17:38

Hello,

Here's a snip from spirit docs 
<<
Rules straddle the border between static and dynamic C++. 
In effect, a rule transforms compile-time polymorphism 
(using templates) into run-time polymorphism (using virtual 
functions). This is necessary due to C++'s inability to 
automatically deduce the type of an arbitrarily complex type 
in the right-hand side (rhs) and pass it on to the left-hand 
side (lhs) of an assignment. 
>>

I was trying to avoid virtual function at all costs. If only there 
was a way in C++ to get the type of the rhs and pass it into 
the lhs, I wouldn't have needed rules. In fact you can do away 
with rules if you want to do more typing. Example:
 
Alternative<ChLit<>, Sequence<ChLit<>, ChLit<> > > rule = a | b >> c;
 
Assuming a, b and c are ChLits. It's the typing (pun intentional) 
that necessitated Rules.
 
There was a proposal in comp.std.c++ to reuse the auto 
keyword to do this. With this extension, we could do:
 
auto rule = a | b >> c;
 
And Spririt will completely be static.

Does anyone have a better way of doing this?

Thanks,
Joel de Guzman