Conversion of one object type to another

[Ram]

Hi,

I have a container of base pointers and I want to generate a container
of derived class pointers from it by casting each pointer of base class
to a pointer of derived class. Is it possible to do it using some
algorithm and function object from STL?

e.g.

std::vector<Base*> base_vector;
std::vector<Derived*> derived_vector;

// populate base vector..

I would like to say something like,

std::transform(base_vector.begin(), base_vector.end(),
std::back_inserter(derived_vector), dynamic_cast<Derived*>());

To be short, I am looking for a function object which can convert one
type of object to another. I think cast operators don't behave like
function objects so they can't be passed to stl algorithms.

Thanks
Ram

 

[Victor Bazarov]

I have a container of base pointers and I want to generate a container
of derived class pointers from it by casting each pointer of base class
to a pointer of derived class. Is it possible to do it using some
algorithm and function object from STL?

e.g.

std::vector<Base*> base_vector;
std::vector<Derived*> derived_vector;

// populate base vector..

I would like to say something like,

std::transform(base_vector.begin(), base_vector.end(),
std::back_inserter(derived_vector), dynamic_cast<Derived*>());

To be short, I am looking for a function object which can convert one
type of object to another. I think cast operators don't behave like
function objects so they can't be passed to stl algorithms.

Just roll your own:

template<class T> struct dynamic_caster {
template<class U> T operator()(U u) const
{ return dynamic_cast<T>(u); }
};

....
std::transform(...
, dynamic_caster<Derived*>());


V

 

[Pete Becker]

Just roll your own:

template<class T> struct dynamic_caster {
template<class U> T operator()(U u) const
{ return dynamic_cast<T>(u); }

return dynamic_cast<T>(*u);

The function call operator will be called with an iterator, and the code
needs to dereference it to get to the stored pointer.

 

[Victor Bazarov]

return dynamic_cast<T>(*u);

The function call operator will be called with an iterator, and the code
needs to dereference it to get to the stored pointer.

Absolutely. Thank you.

 

[Victor Bazarov]

return dynamic_cast<T>(*u);

The function call operator will be called with an iterator, and the code
needs to dereference it to get to the stored pointer.

Really? On an iterator? I thought it was specified as op(*(blah)), OW
dereferencing the iterator before calling the op...

V

 

[Pete Becker]

Really? On an iterator? I thought it was specified as op(*(blah)), OW
dereferencing the iterator before calling the op...

You're right. Ignore my correction.

 

[Frank Chang]

Ram, The class Base must have at least one virtual function for this to
compile.

 

[Ram]

Ram, The class Base must have at least one virtual function for this to
compile.

Exactly Frank, those assumptions are supposed to be met by Base.

 

[Ram]

To be short, I am looking for a function object which can convert one

Just roll your own:

template<class T> struct dynamic_caster {
template<class U> T operator()(U u) const
{ return dynamic_cast<T>(u); }
};

Thanks Victor, I have already done something similar. But as mentioned
in my OP, I was wondering if the standard library already provides some
function/functor for this.

Ram