[wave::token_type] Checking if the token_type instance is empty
Hello Hartmut, 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 ;) With Kind Regards, Ovanes Markarian
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
Hartmut, many thanks for your understanding. Just a small question: Isn't it better to have empty() function like all other STL containers do? string, vector, ... they all provide empty. I don't think this is really self explanatory to the user to have is_eoi and sometimes can be confusing, because as I understand EOI means End of Input. But if I construct a token instance, there is no end of input, it is empty. It still can internally point to EOI. What is your opinion? But I am also very happy with is_eoi ;) With Kind Regards, Ovanes On Tue, April 3, 2007 16:02, Hartmut Kaiser wrote:
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
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Hartmut Kaiser -
Ovanes Markarian