From: Joel de Guzman (joel_at_[hidden])
Date: 2005-10-23 10:15:38
Korcan Hussein wrote:
> "Larry Evans" <cppljevans_at_[hidden]> wrote in message
>>On 10/22/2005 06:58 AM, Larry Evans wrote:
>>Are you suggesting this as an alternative to Spirit subrules?
> Doesn't need to replace subrules but could be an alternative implementation
> for them, if you read the part:
> ... It might not be apparent but behind the scenes, plain rules are actually
> implemented using a pointer to a runtime polymorphic abstract class that
> holds the dynamic type of the parser assigned to it. When a Spirit
> expression is assigned to a rule, its type is encapsulated in a concrete
> subclass of the abstract class. A virtual parse function delegates the
> parsing to the encapsulated object.
> Rules have drawbacks though:
> It is coupled to a specific scanner type. The rule is tied to a specific
> scanner [see The Scanner Business].
> The rule's parse member function has a virtual function call overhead that
> cannot be inlined.
That quote pertains to (type-erased rules) not subrules.
Subrules in Spirit are completely static. No type erasure.
Please read the http://www.boost.org/libs/spirit/doc/subrules.html
carefully. Read below the lines that you have quoted. Those lines
you quoted were there just to explain the problems of type-erased
I'm quite interested if you have a better alternative. For example,
how do you write the Spirit calculator using your scheme:
rule<> group, factor, term, expression;
group = '(' >> expression >> ')';
factor = integer | group;
term = factor >> *(('*' >> factor) | ('/' >> factor));
expression = term >> *(('+' >> term) | ('-' >> term));
-- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net
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