On Thursday 26 May 2005 12:06, Hans Maartensson wrote: > In a program I had a recursive definition like: > > type sometype = record > n: longint; > p: ^sometype > end;
This was never allowed in Pascal, AFAIK. The standard solution is to define the pointer type first: |type | ptr_sometype = ^sometype; |type | some_type = | record | p : ptr_sometype; | ... | end; > Also the following call to a win32 API function is not allowed any > more: > > invalidaterect(windows, 0, true); > > The error is that the 2nd parameter should be of type 'rect'. Have you actually tried "InvalidateRect (windows, NIL, True);"? > The 2nd parameter in this example must be of 'var' type, which means > that it is the pointer to the parameter that is transferred to the > function. Transferring a nil pointer is in pascal language the same > as leaving the parameter undefined. But that is not possible in > FreePascal, is it? It is, because of function overloading: function InvalidateRect(hWnd:HWND; var lpRect:RECT; bErase:WINBOOL):WINBOOL; external 'user32' name 'InvalidateRect'; function InvalidateRect(hWnd:HWND;lpRect:LPRECT; bErase:WINBOOL):WINBOOL; external 'user32' name 'InvalidateRect'; So the second form takes a pointer, thus passing NIL should be perfectly allowed, AFAICS. > Finally I would like to ask about the following. > The compiler does not allow a procedure definition like: > > procedure someproc(p: ^double); > > whereas the following is perfectly possible: > > type Tpdouble = ^double; > procedure f(p: Tpdouble); > > Is there a good reason for this? Why isn't ^double a valid type > everywhere? Because type1 = ^double; type2 = ^double; should be considered different types. So if you define the type in the procedure declaration, you couldn't call it, just because you can't declare a variable of the same type for the argument. The only allowed argument would be NIL, which I think is a little bit pointless. BTW, why don't you use "procedure f(const/var/out p : double);" instead to get rid of as much pointers as possible and use the right parameter modes which also have the side effect of being more self documenting? Vinzent. _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
