Re: Characterize parameters by type

From:

mzdude <jsanga@cox.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Mon, 29 Jun 2009 23:09:40 CST

Message-ID:

<24faf9f7-57cd-48a0-9de0-e941b233f71a@j20g2000vbp.googlegroups.com>

On Jun 29, 5:31 pm, Rune Allnor <all...@tele.ntnu.no> wrote:

Hi all.

I have an application written in C++ that needs to be
interfaces with matlab. The interface routine needs to
take a number of untyped parameters from matlab
domain, and return a typed object to be passed to the
C++ business routine.

The parameters are:

par1 - vector of either 2 or 4 doubles
par2 - vector of 2 doubles

I would like to implement a test TestParameters that
returns an object which type depends on the combination
of the parameters:

if (par1.size() == 2)
{
     if (par2(1) > par2(2))
         // return object of class Case1Class
     else
         // return object of class Case2Class}

else if (par1.size() == 4 )
{
     if (par2(1) > par2(2))
         // return object of class Case3Class
     else
         // return object of class Case4Class}

else
{
     return 0;

}

I can't see how to wrap this into a function that can
be called from the interface routine.

Any suggestions?

A couple.
    Create a class factory that uses polymorphism
    Check out boost::any

// Warning all code untested
class Base {};

class Case1Class : public Base {};
class Case2Class : public Base {};
class Case3Class : public Base {};
class Case4Class : public Base {};

// pick the pointer type that best works for you
boost::shared_ptr<Base>
MyClassFactory( X const &par1, Y const &par2 )
{
   Base *p = 0;
   if (par1.size() == 2)
   {
     if (par2(1) > par2(2))
       p = new Case1Class;
    else
       p = new Case2Class;
   }
   else if (par1.size() == 4 )
   {
     if (par2(1) > par2(2))
       p = new Case3Class;
     else
       p = new Case4Class;
   }
   return p;
}

/////////////// OR /////////////////

struct X { int a;};
struct Y { float b;};

boost::any MyClassFactory(int a)
{
    if(a)
       return boost::any( X() );

    return boost::any( Y() );
}

void SomeFunct()
{
    boost::any b = MyClassFactory(0);
}

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