[fpc-devel] Bug in FPC and declaring distinct types

[Michael Van Canneyt]

On Thu, 18 Sep 2008, Florian Klaempfl wrote:

> Michael Van Canneyt schrieb:
> > 
> > On Thu, 18 Sep 2008, Graeme Geldenhuys wrote:
> > 
> > > Hi,
> > >
> > > I was following a discussion in the delphi.non-technical newsgroup.
> > > They raised an issue about distinct types. I tried the following
> > > example under FPC and unexpectedly, FPC doesn't raise any errors!
> > >
> > > If you declare a distinct type as follows:
> > >   type TMyInteger = type Integer;
> > >
> > > The type TMyInteger <> Integer so you are not supposed to be allowed
> > > to assign one to the other. Yet you can. See the following program.
> > 
> > But obviously delphi also allows it ? It compiles everything,
> > just not as a var parameter.
> > 
> > The whole 'Type' thing is a bit ridiculous: the only reason they did it
> > is so they can have different type pointers in the RTTI for something which
> > is the same 'type' anyway. For the rest it is extremely badly designed, and
> > not really consistent. It serves no purpose. FPC introduced it to be able to
> > compile Delphi code, no other reason.
> 
> This is not true. The main purpose is to be able to overload
> functions/operators:
> 
> type
>   TUTF8String = type ansistring;

Well, that was not so for delphi. The delphi help explicitly says:

"if your purpose in defining a new type is to utilize runtime type
information--for example, to associate a property editor with properties of
a particular type--the distinction between "different name" and "different
type" becomes important. In this case, use the syntax"

I've lived with this knowledge for years :-)

> 
> enables you to overload all procedure already defined for ansistrings with
> UTF8String functions but reusing ansistring support functionality and this is
> supported for years. Because nobody used this yet to make an utf-8 unit, I
> never took the unicode string support serious :)

Aha, in that case, you should have told me this so I could document it !

I cannot see inside your head, you know :-)

Maybe make a backup of your brain and send it to me ? 
A 1Tb. external disk is no longer so expensive :-)

Michael.