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Guest
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 Posted: Thu Apr 05, 2007 11:22 pm Post subject: Typecasting |
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What is the meaning of this syntax :
Objectname1 := ClassName (Objectname2) ;
Thanks for your help. |
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Craig Stuntz [TeamB]
Guest
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| Posted: Fri Apr 06, 2007 1:17 am Post subject: Re: Typecasting |
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amir.e (AT) softhome (DOT) net wrote:
| Quote: | What is the meaning of this syntax :
Objectname1 := ClassName (Objectname2) ;
|
It tells the compiler: "I am absolutely positive that Objectname2 is
of a class which can be assigned to a reference of the declared type of
Objectname1, so you should ignore all type checking and just go ahead
and do the assignment."
E.g.:
var
Obj: TObject;
Foo1, Foo2: TFoo;
begin
Foo1 := TFoo.Create;
Obj := Foo1; // OK; TFoo is a subclass of TObject
Foo2 := Obj; // not OK; TObject <> TFoo, nor does TObject
// inherit from TFoo
Foo2 := TFoo(Obj); // OK, since we know that Obj currently
// contains an instance of TFoo
This is dangerous if you're not absolutely positive of the type of the
instance.
--
Craig Stuntz [TeamB] · Vertex Systems Corp. · Columbus, OH
Delphi/InterBase Weblog : http://blogs.teamb.com/craigstuntz
IB 6 versions prior to 6.0.1.6 are pre-release and may corrupt
your DBs! Open Edition users, get 6.0.1.6 from http://mers.com |
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Amir
Guest
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| Posted: Fri Apr 06, 2007 8:12 am Post subject: Re: Typecasting |
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On Apr 6, 12:17 am, "Craig Stuntz [TeamB]" <craig_stu...@nospam.please
[a.k.a. acm.org]> wrote:
| Quote: | ami...@softhome.net wrote:
What is the meaning of this syntax :
Objectname1 := ClassName (Objectname2) ;
It tells the compiler: "I am absolutely positive that Objectname2 is
of a class which can be assigned to a reference of the declared type of
Objectname1, so you should ignore all type checking and just go ahead
and do the assignment."
E.g.:
var
Obj: TObject;
Foo1, Foo2: TFoo;
begin
Foo1 := TFoo.Create;
Obj := Foo1; // OK; TFoo is a subclass of TObject
Foo2 := Obj; // not OK; TObject <> TFoo, nor does TObject
// inherit from TFoo
Foo2 := TFoo(Obj); // OK, since we know that Obj currently
// contains an instance of TFoo
This is dangerous if you're not absolutely positive of the type of the
instance.
--
Craig Stuntz [TeamB] · Vertex Systems Corp. · Columbus, OH
Delphi/InterBase Weblog :http://blogs.teamb.com/craigstuntz
IB 6 versions prior to 6.0.1.6 are pre-release and may corrupt
your DBs! Open Edition users, get 6.0.1.6 fromhttp://mers.com
|
Dear
Thanks for your complete answer,
you explained clearly . |
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