Re: [fpc-pascal] constructor as procvar

[Michael Van Canneyt]

On Sat, 20 Mar 2010, David Emerson wrote:

How can I obtain a class type variable from an instance? I want to
create a second instance of the same descendant class (via the
constructor, which will take some parameters and make the new instance
unique)

Try using Instance.ClassType. Something like:

Var
  C : t_mammal_class;
  MyClone : T_mammal;

begin
  C:=t_mammal_class(Instance.ClassType);
  MyClone:=C.Create;
end;


Michael.

Tobject.classtype returns TClass (class of TObject) which I first
assumed would work great. However I cannot seem to do a type conversion
from TClass to t_mammal_class (class of t_mammal)! So I am stuck here.

I tried just using TClass and skipping t_mammal_class, but then I can't
use my overriden constructor that takes special parameters.

Thanks in advance,
David.


On Fri 19 Mar 2010, David Emerson wrote:

Florian Klaempfl wrote:

Constructor procvars are indeed not supported but the way to achieve
what you want is to use class type variables

  t_mammal_class = class of t_mammal;

  function find_or_create_animal (color : byte;
      pass_mammal_type : t_mammal_class) : t_mammal;

  brown_pig := t_pig (pig_pen.find_or_create_animal (brown, t_pig));

ah, that is exactly what I need. Works perfectly. Thanks much.

~D.

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