I'd like to pass a constructor as a procvar. Don't know if this is
possible. Here is some silly illustrative code that doesn't work:
{$mode objfpc}
uses classes, sysutils;
type
t_mammal = class
public
constructor create (color : byte); virtual;
end;
t_pig = class (t_mammal)
// some fields, methods
end;
// the following fails:
t_mammal_creator = t_mammal.constructor (color : byte) of object;
// a list of animals...
t_barnyard = class
public
function find_or_create_animal (color : byte;
pass_create : t_mammal_creator) : t_mammal;
end;
constructor t_mammal.create (color : byte);
begin
end;
function t_barnyard.find_or_create_animal (color : byte;
pass_create : t_mammal_creator) : t_mammal;
begin
// look for the animal within the list. if not found:
result := pass_create (color);
end;
const
brown = 18;
var
pig_pen : t_barnyard;
brown_pig : t_pig;
begin
pig_pen := t_barnyard.create;
brown_pig := t_pig (pig_pen.find_or_create_animal
(brown, @t_pig.create));
end.
As you can (probably) see, I would like t_barnyard to be able to create
any descendant of t_mammal. In the above example, I want it to create a
brown pig if it doesn't find one, so I tried to pass the t_pig
constructor, along with the brown parameter that said constructor will
require. But I can't figure out the syntax. Perhaps this kind of thing
is not supported?
Thanks!
~David.
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