Peter Schorn wrote:

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 similar problem occurs when using procedural parameters with untyped parameters:

program testsort1;

procedure qsort( const var data; membercount, membersize: sizetype; function comparator( const var e, f): cinteger); external name 'qsort';

type elementtype = integer;

function compare( const var i, j : elementtype): cinteger; begin if i = j then compare:= 0 else if i < j then compare:= -1 else compare:= +1 end;

const k = 10; var a: array[ 1..k] of elementtype value ( 4, 9, 6, 1 ,3, 4, 4, 6, 8, 7); n: integer; begin writeln( 'unsorted'); for n:= 1 to k do writeln( a[ n]); qsort( a, k, SizeOf( elementtype), compare); writeln( 'sorted'); for n:= 1 to k do writeln( a[ n]) end.

or the generic Pointer type:

program testsort2;

procedure qsort( pdata: pointer; membercount, membersize: sizetype; function comparator( p1, p2: pointer): cinteger); external name 'qsort';

type elementtype = integer; elementptr = ^elementtype;

function compare( p1, p2: elementptr): cinteger; begin if p1^ = p2^ then compare:= 0 else if p1^ < p2^ then compare:= -1 else compare:= +1 end;

const k = 10; var a: array[ 1..k] of elementtype value ( 4, 9, 6, 1 ,3, 4, 4, 6, 8, 7); n: integer; begin writeln( 'unsorted'); for n:= 1 to k do writeln( a[ n]); qsort( @a, k, SizeOf( elementtype), compare); writeln( 'sorted'); for n:= 1 to k do writeln( a[ n]) end.

The first program also shows another problem

program testsort1; {<- syntax error before `;'}

which may be due to a compiler problem with untyped "const var" parameters.

Regards.

Adriaan van OS

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.

1. Mutual recursive object type declaration

As long as you aren't inheritting from another object, you can use a forward object type declaration in both GPC and CodeWarrior Pascal for mutually recursive onject type declarations.

program prog1; { compile with gpc --mac-pascal prog1.pas } type

t2 = object; forward;

 t1 = object
     function f: t2; { error: unknown identifier `t2' }

{ above works in CodeWarrior Object Pascal as objects are always references } end;

 t2 = object
     function g: t1;
 end;

function t1.f: t2; begin f := nil; end; function t2.g: t1; begin g := nil; end; begin end.

As a workaround this can be solved by introducing a common super class and subsequent casting.

With the added forward object declaration for t2, GPC compiles the example with no errors.

Gale Paeper gpaeper@empirenet.com

Peter Schorn wrote:

3. Cast in with statement

program prog3; { compile with gpc --mac-pascal prog3.pas } type baseType = object end;

derivedType = object(baseType)
    procedure f;
end;

procedure derivedType.f; begin end;

var a: baseType; b: derivedType;

begin new(b); a := b; derivedType(a).f; { ok } with derivedType(a) do { warning: `with' element is not a constant or an lvalue } f; { error: invalid lvalue in method call } { error: function call used as a statement } end.

A workaround is to use a temporary variable for the with statement.

This compiles with gpc-20060325 (but not with the compiler at my website, based on gpc-20051116)

Regards,

Adriaan van Os