Re: [Boost-users] [wave::token_type] Checking if the token_typeinstance is empty

From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2007-04-03 10:02:27

Ovanes,

> I have a question and may be small interface change to the 
> token_type. Currently there is no "legal" way to check if a 
> token type instance is empty, than using token_id operator 
> and comparing it with T_EOI (which is not really documented, 
> available in the header and default ctor of impl::token_data only).
> 
> Why did I need it:
> 
> I have a state machine class which preserves the look ahead. 
> Now when I construct the state machine, the look ahead is 
> default constructed. In particular states I have to 
> distinguish if there is look ahead available or not and take 
> some actions accordingly. Now I would need to rely on the 
> following comparison:
> 
> BASEID_FROM_TOKEN(T_EOI)==tok.operator token_id();
> 
> Instead it would be more flexible to write tok.empty(). I am 
> not sure if this convinces you, but at least T_EOI should be 
> documented (I am still using old documentation 1.33.1). The 
> docs should also state that empty token has this type. On the 
> other hand I don't know where else T_EOI is used and how to 
> distinguishe this case then. I would appreciate the empty 
> member function, which can greatly ease the life ;)

I added an 'is_eoi()' function to the token types and will change the
documentation soon. It's in the Boost CVS::HEAD.

HTH
Regards Hartmut