Re: Interface Question

alanglloyd@xxxxxxx wrote:
Inheritance for IShellLink, IPersist, and IPersistFile is declared as
...

IShellLink = interfac(IUnknown) etc etc
IPersist = interface(IUnknown) etc etc
IPersistFile = interface(IPersist) etc etc

and I then see code of ...

var
ObjectIF : IUnknown;
ShellLinkIF : IShellLink;
PersistFileIF : IPersistFile;

begin

ObjectIf := CreateComObject(CLSID_Shellink);
ShellLinkIF := ObjectIF as IShellLink;
// do something with ShellLinkIF
PersistFileIF := ObjectIF as IPersistFile;
// do something with PersistFileIF

Now IShellLink has _none_ of the methods of IPersist or IPersistFile,
so _how_ can an IShellLink be typecast to an IPersistFile. Or is the
COM object of ObjectIF somehow re-created as an IPersistFile when
type-cast as such.

Hi !
The expression "ObjectIF as IPersistFile" is implemented through the
implementing class of ObjectIf's QueryInterface method. That's the "as"
operator when used on IUnknowns.
It's confusing. I know. (Maybe I too got it all wrong now ?)

--
Bjørge
'93 TDM850
bjorge@xxxxxxxxxxxx


.

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