C++Talk.NET

hydrajak@yahoo.com · Guest

Hello group,

This is a pretty basic question....

I'm using Loki Functors and I want to store them in a generic container
(like vector or map). The problem is that each kind of functor is-a
different type because of the template paramaters. So I had the bright
idea to hack Loki and make Functor inheret from a

class FunctorInterface{};

so now I can store a functor in a vector as a FunctorInterface*. Sweet.
However, I can't USE a FunctorInterface because it is an empty class,
so I need to convert the FunctorInterface* back to the right kind of
Functor.

Here is how it is getting used....

Larry l;
Functor<void, TYPELIST_1(string) > fun2(&l,Larry::foo);

CommandManager<LocalExecutionPolicy> cMgr;
cMgr.registerCommand("Larry's Command",fun2);
FunctorInterface* f = cMgr.retreiveCommand("Larry's Command");
int someInt;
cMgr.triggerCmd<void>(f,someInt);

Now as we can see, that last line is a clear error. fun2 takes a string
not an int. if you tried:

fun2(someInt);

you would get a compile error.

Without going into too much detail, here is the policy that is
responsible for executing the functor in CommandManager:

template<typename R,typename P1>
R LocalExecutionPolicy::triggerCmd(Loki::FunctorInterface* f,P1 param1)
{
Loki::Functor<R,TYPELIST_1(P1)>* fun = static_cast<
Loki::Functor( f );
return (*fun)(param1);
}

So my problem is that the static_cast happly converts the f* into a
Functor, but with a TYPELIST_1( int ) instead of a TYPELIST_1( string
) like I want. Now.... I COULD add a virtual descrutor to
FunctorInterface and use a dynamic_cast but:

1) That is slow
2) That is run time error checking, not compile time.

I need some way when I call CommandManager::registerCommand() to save
the type of the TList so that I can compare it later to the
CommandManager::Trigger() call. I would like this all to happen at
compile time so that bad Trigger calls simply won't compile. I have
stared at Chapter 2 of Modern C++ Designs over and over and over and I
think I'm missing the obvious.

Thanks,
Larry E. Ramey

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

Andreas Magnusson · Guest

Haha, this is funny, I recently posted here about an article I have
written that describes just how to do what you want. Except I don't use
Loki::Functor, but it's possible you can change that if you really want
to. I have also not had the time to publish the whole source code to
the article but I hope to do so soon.

My article describes how to store functions with different types and
how to invoke them by deriving all their parameters using one
super-parameter (this is since you can't invoke a function if you don't
give it the correct parameters).

Anyway, here's a link to my article:

http://amag.rotd.org/tutorials.php

Cheers,
Andreas

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

msalters · Guest

hydra... (AT) yahoo (DOT) com schreef: