Re: default constructor and class

[Michael Goffioul]

On Mon, Jul 8, 2013 at 3:34 PM, Marco Vassallo <address@hidden> wrote:

________________________________
> Date: Mon, 8 Jul 2013 15:27:45 -0400
> Subject: Re: default constructor and class
> From: address@hidden
> To: address@hidden
> CC: address@hidden
>
> On Mon, Jul 8, 2013 at 3:20 PM, Marco Vassallo
> <address@hidden<mailto:address@hidden>> wrote:
> Hi all,
>
> for the fem-fenics pkg I'm creating a new class, and I thus add as
> private members
>
>    DECLARE_OCTAVE_ALLOCATOR;
>    DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA;
>
> and also the DEFINE counterpart,
>
> which requires the class to have a default constructor (right?)
>
> The problem is that one of the parent class from which I derive my own class
> doesn't provide a default constructor. Example
>
> class B: public octave_base_value, public A
> {
>    B(): octave_base_value(), A(), B() {} //error: A() not available
>
>    private:
>    A my_element;
>    DECLARE_OCTAVE_ALLOCATOR;
>    DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA;
> }
>
> How can I manage it?
>
> I'm not sure I understand your construct correctly, but is it
> intentional that B inherits from A *and* contains a A object
> (my_element)? Can't you get rid of the inheritance from A and just have
> the my_element member?
>
> Michael.

This class should be a wrapper for the A class.
Even if I avoid deriving from A,

 class B: public octave_base_value
{
 B(): octave_base_value() {} //error: default constructor for my_element not available
 
 private:
 A my_element;
 DECLARE_OCTAVE_ALLOCATOR;
 DECLARE_OV_TYPEID_FUNCTIONS_AND_DATA;
 }

I still need a constructor for my_elements, and as it is an object of type A I
need to initialize it somehow.                                    

Why don't you do the following instead for the default constructor of class B:

B(): octave_base_value(), my_element(<whatever_argument>) {}

Michael.