[fpc-pascal] const parameter writeable
fpc505 at z505.com
Tue May 2 18:51:59 CEST 2006
> > >
> > > 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;
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
> 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
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.
TSomeClass = class
procedure ChangeClass(const SomeClass: TSomeClass);
SomeClass.a:= 'string A';
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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