On 20/08/2013 02:44, Xiangrong Fang wrote:
Hi All,
I am reading this document:
http://www.freepascal.org/docs-html/ref/refsu29.html and doing an
experiment with the following code:
program project1;
{$mode objfpc}{$H+}
type
TBase = class
constructor Create; virtual;
end;
TDerived = class(TBase)
constructor Create; override;
end;
....
The problem is, it makes NO DIFFERENCE at all in the following cases:
CASE 1:
TBase.Create;
TDerived.Create;
CASE 2:
TBase.Create; virtual;
TDerived.Create; virtual;
CASE 3:
TBase.Create; virtual;
TDerived.Create; override;
According to the document, "inherited" cannot be used in non-virtual
methods, and it is wrong to use virtual in sub-class. But my test
shows the contrary. BTW, I am running Linux on 64bit platform.
Using virtual with constructor makes a difference, if you use "class of"
types
type
TBaseClass = class of TBase;
TDerivedClass = class of TDerived;
Var
bc: TBaseClass;
begin
bc:= TBase;
bc.create;
bc:= TDerived;
bc.create; // will call Tderived.create, but only in case 3
end;
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