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From: Peter Schorn
Subject: GPC and CodeWarrior Object Pascal
Date: 20 Apr 2006, 18:46:32

Waldek Hebisch wrote:
> Peter Schorn wrote:
>> Dear all,
>>
>> while porting from CodeWarrior Object Pascal to GPC I noticed the 
>> following differences which might be worthwhile to address in GPC.
>>
>>
>> 2) Procedure type assignment compatibility with specialized parameters
>> program prog2; { compile with gpc --mac-pascal prog2.pas }
>> type
>>      baseType = object
>>      end;
>>
>>      derivedType = object(baseType)
>>      end;
>>
>> procedure p1(x: baseType); begin end;
>> procedure p2(x: derivedType); begin end;
>> var pv: procedure(x: baseType);
>> begin
>>      pv := p1;
>>      pv := p2; { error: incompatible types in assignment }
>> end.
>>
>> A workaround is to declare the x in p2 as baseType and perform a cast in 
>> the body of p2.
>>
>>
> 
> Assigning p2 to pv is unsafe (I allows breaking type rules). Consider:
> 
> program unsafe;
> type
>      baseType = object
>      end;
> 
>      derivedType = object(baseType)
>      procedure m;
>      end;
> 
> procedure derivedType.m;
> begin
> end;
> 
> var pv: procedure(x: baseType);
>     v: baseType;
> 
> procedure p2(x: derivedType);
> begin
>   x.m
> end;
> 
> begin
>   new(v);
>   pv := p2; { error: prevents wrong call }
>   pv(v)
> end
> .
> 
> The only place which prevents wrong call is assignment to pv. Do
> CodeWarrior accept the program above?
[ ... ]

Thanks - I see. CodeWarrior compiles the program above without any error 
message but the program crashes when executed (not surprisingly anymore).

Peter Schorn
mailto:peter.schorn@acm.org

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