RE: [Boost-users] Need a method to compare types of data objects atruntime

From: Marcin Tustin (mt_at_[hidden])
Date: 2005-04-25 04:29:10

const type_info& type = typeid(*v); Comparable based on string
representation. Part of standard. Header <typeinfo>. 

> -----Original Message-----
> From: Stephen Torri [mailto:storri_at_[hidden]] 
> Sent: 24 April 2005 19:46
> To: boost
> Subject: [Boost-users] Need a method to compare types of data 
> objects atruntime
> 
> If I have a abstract class with two classes that implement it 
> how can I make a check that tests for the type of the 
> implementation classes?
> 
> For example:
> 
>         class Base {
>         public:
>         	virtual void run (){}
>         	virtual void stop (){}
>         };
>         
>         class Gas_Pedal : public Base {
>         public:
>         	virtual void run (){}
>         	void set_rate (unsigned int);
>         private:
>         	unsigned int m_rate;
>         };
>         
>         class Brake_Pedal : public Base {
>         public:
>         	virtual void stop (){}
>         	void set_pressure (unsigned int);
>         private:
>         	unsigned int m_pressure;
>         };
> 
> When I have a client that receives a Base object I want to be 
> able to check at run-time. So that if I am expecting a 
> Gas_Pedal object and I receive something else I can perform 
> some recovery action. The software I am designing contains an 
> untold number of arrangements of items. Each item expect a 
> distinctive input type. If it receives something that it does 
> not know how to handle or need I want to throw an error.
> 
> In order to do this I would like to do something like:
>         
>         void process (Base* sobj)
>         {
>         	if (! (isExpectedType(sobj))
>         	{
>         		throw NotForMeException ();
>         	}
>         
>         	Brake_Pedal* bp = dynamic_cast<Brake_Pedal>(sobj);
>         	bp.set_pressure (50);
>         }
> 
> So perhaps my design is flawed that I am running into this 
> situation. I am attempting to keep the interface for the Base 
> class simple. The underlying types could have different data 
> and access methods because they differ so widely in what they 
> will do. This example was given to keep things simple.
> 
> Stephen
> 
> 
>