> > >
> > > But in this case I'm wondering why you want to give a pointer instead
> > > of the real type?
> >
> >
> > did you mean this ? :
> >
> > procedure ChangeRec1(const Rec: TSomeRec);
> > begin
> > Rec.a:= 'string A';
> > end;
>
> Yes.
Well, this is a Precord. That doesn't work. That is why I was confused.
>
> > Because I can't pass a PSomeRec to that function, only a TSomeRec
>
> Where is the problem? If you allocated the memory by new() as in your
> example you could call
> ChangeRec1(RecPtr^);
> and the compile (hopefully) uses the pointer.
Yes, but you are repeating what Jonas says - if you would have told me this
first, you
would have gotten the brownie points. But Jonas gets them. :-)
>
> But in this case you will get an compiler error because you can't
> change a constant value.
>
> It seemed that I didn't get the point from your original mail:
> Name the procedure CHANGERec1 and change a value but declare the
> parameter as constant.
I was asking why I could write to a const. But in fact I was not writing to the
CONST, I
was actually writing to the const data it pointed to. With SomeRec^ I cannot
write to
const. Problem solved.
I was using sloppy Delphi style code without ^ since Delphi enforces this
sloppy style of
coding, and now I know why not to use sloppy delphi style code.
What I was confused about was why you recommended TSomeRec when we are dealing
with
PSomeRec.
I also stated that I knew you can pass TSomeClass as a const, you can still
access it's
properties even though it is a const.
program project1;
{$mode objfpc}{$H+}
type
TSomeClass = class
a: string;
b: string;
end;
procedure ChangeClass(const SomeClass: TSomeClass);
begin
SomeClass.a:= 'string A';
end;
var
SomeClass: TSomeClass;
begin
someclass:= TSomeClass.create;
ChangeClass(someclass);
writeln(someclass.a);
someclass.free;
readln;
end.
This is normal, because we are passing a pointer when dealing with a class -
not passing
the class contents. Which is really what I should have thought about before
asking the
question, because I have discovered you can write to a const class *contents*
before.
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