C++Talk.NET

Dirk Gregorius · Guest

Dear group,

when I write a factory function that creates a range of objects how do
I parameterize the container class? Example:

class Object { /* Implementation */ };

How do I implement a factory function that creates exactly n objects?
This function seems obvious:

bool make_objects( std::vector<Object>& objects );

But what if I dont't want to force a client to use std::vector<> and
the client wants to pass a C array or boost::array? Would such an
implementation make sense as well:

template<OuputIterator>
bool make_objects( OutputIterator result ); // must be able to store 4
objects

This will force the client to allocate enough memory, which will make
the code more error prone IMO. And what about when the design changes
and I need dynamic memory allocation? So how do I return a range of
objects where the size of the range will be first known at run-time?

template<Sequence>
bool make_objects( Sequence& collection );

Do I have to constraint that the passed collection is at least
assignable ( like models of the standard sequence concept ), such that
I can do something like this:

template<Sequence>
bool make_objects( Sequence& sequence )
{
std::vector coll( NUM_ELEMENTS );

//Create objects and assign them to coll...

// IIRC the standard defines that a model of sequence needs to
implement
// the assign() function - correct?
sequence.assign( coll.begin(), coll.end() );

return true;
}

How do I handle such situations to gain maximum style points :-)

I wish all of you a happy new year!

Regards,

-Dirk

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ox · Guest

Design with OutputIterator seems pretty feasible to me;
std::back_insert_iterator & Co. can add even more flexibility. And do
not forget that you can always define your own iterator classes (or
adaptors).

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Victor Bazarov · Guest

Dirk Gregorius wrote:

ox · Guest

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Victor Bazarov · Guest

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Dirk Gregorius · Guest

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jeffz_2002@yahoo.com · Guest

(untested solution...) I was going to suggest creating an Adaptor
pattern implementation that could be templated out for the various
cases (stl containers, arrays, etc), but I think that this will boil
down to some kind of back_insert iterator as ox suggested. You could
then use a policy to do a compile time check of the type of the
destination, which would then handle the filling of the container
appropriately.

Good luck, let us know how it turns out.
Jeff

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Maxim Yegorushkin · Guest

Dirk Gregorius wrote: