Re: A polymorphic YYSTYPE for C++ (instead of the %union)

[Hans Aberg]

On 25 Jun 2007, at 16:57, Akim Demaille wrote:

>  I was hoping that someday someone would implement a similar
> feature, but (i) without the Boost dependency, and (ii) without this
> additional space and time cost.

I think that the most important thing is to implement the typed  
default actions, that is, instead of the current untyped $$ = $1, one  
should have $<type>$ = $<type1>1. That is, the different default  
actions should be collected according to type, and put into the  
parser "switch" statement. I think this must be done, regardless  
which typed method is used, and the difference is essentially then  
down to how to extract the different types of the YYSTYPE. Michiel De  
Wilde pointed out another, C++ specific problem, namely that template  
types may involve the pointed braces "<" and ">". So if one should  
use a M4 macro to handle these different statically typed YYSTYPEs  
that may be used with C++ via a M4 macro, some extensions to the  
handling of type identifiers might be needed. I am not sure of this  
though: these pointed brackets might still be put into some M4 macro,  
and then the types used in the grammar might be still be just the  
usual C/C++ labels.

  Hans Aberg