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

[Yury Sidorov]

From: "Florian Klaempfl" <florian at freepascal.org>
> 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;
>
> 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 :)

Yes. But it works only partially. For example the following code is 
not compilable:

//------
type
  TUTF8String = type ansistring;

procedure DoTest(const s: ansistring); overload;
begin
end;

procedure DoTest(const s: TUTF8String); overload;
begin
end;

begin
  DoTest('1234');
end.

//------

Yury Sidorov.