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Jeremy · Guest

In a thread on the iobserver pattern last month there was reference to
strong and weak pointers or references. A quick search doesn't reveal a
definition. Can someone enlighten me on what these are?

Jeremy

Bob Dawson · Guest

"Jeremy" <jeremy> wrote

Joanna Carter [TeamB] · Guest

"Jeremy" <jeremy> a écrit dans le message de news:
448066f2 (AT) newsgroups (DOT) borland.com...

| In a thread on the iobserver pattern last month there was reference to
| strong and weak pointers or references. A quick search doesn't reveal a
| definition. Can someone enlighten me on what these are?

In the context of interfaces Delphi for Win32 :

If you have mutual interface references between to objects, then neither of
the objects will be released due to bothe "normal" references being strong -

IOne = interface
end;

ITwo = interface
end;

TOne = class(...IOne)
private
fTwo: ITwo;
public
property Two: ITwo
read fTwo;
end;

TTwo = class(...ITwo)
private
fOne: IOne;
public
property One: IOne
read fOne;
end;

....but if you want to avoid this kind of memory leak, then you replace one
of these references with a Pointer

TTwo = class(...ITwo)
private
fOne: Pointer;
function GetOne: IOne;
public
property One: IOne
read GetOne;
end;

function TTwo.GetOne: IOne;
begin
result := IOne(fOne);
end;

Using the pointer does not increase the reference count on the IOne ref,
therefore breaking the deadlock.

Joanna

--
Joanna Carter [TeamB]
Consultant Software Engineer